When does one plus two equal more than three? When it's the OnePlus 2, the budget self-styled "flagship killer" that's full of top-end features at such an affordable price point that, well, it simply sounds too good to add up.

This 5.5-inch sequel to the original OnePlus One has been through a software revamp (now with the company's OxygenOS 2.0 re-skin over Android), embodies a top-spec Qualcomm Snapdragon 810 processor, and even squeezes in flagship features such as a fingerprint scanner. All starting at just £239, which is touching on mid-range rather than flagship territory.

So what's the compromise? To buy a OnePlus 2 you'll need to sign-up to a waiting list and await an invite, as this budget handset is only available to order online. Having been using one as our main phone for a week there are a few other foibles too. But otherwise, at this price point, has OnePlus just rewritten the flagship rule book?

The thing that most budget phones have is, you guessed it, budget build quality; all plasticky and soap-bar-like naffness. But the OnePlus 2 really doesn't: its metal-frame body encases the 5.5-inch screen in a fashion that's more LG G4 level than something reflective of a £239 phone. If anything, we actually think it looks better than the G4, which we've been using up until this point for a number of months.

Of course there's no leather finery to be seen in OnePlus land, but the rear of the phone has an almost sandpaper like quality to it that, while almost alarming at first, assists with gripping a phone of this scale (other wooden options should be available in the near future).

Pocket-lintP1020116 copy

Otherwise the non-removable rear panel blends seamlessly with the phone body, but at the cost of any internal storage: you can either buy 16GB (£239) or 64GB (£289) as there's no microSD slot. Shame as it's a dual nano SIM device and we feel OnePlus should have taken a lead from Huawei here and offered the second slot as an double-up optional microSD/nano SIM slot (depending on which card type you put in there).

There will certainly be a camp that finds the OnePlus 2 too large, but as other phones have advanced in scale over recent years this size of phone actually feels entirely standard. Its 9.85mm thickness isn't tiny, but it's slimmer than a flagship Windows Phone, its 75mm width is a couple a millimetres less than LG G4, while it feels less bloated than even the Motorola Moto X Play (which, admittedly, is the OnePlus 2's more fun main competitor).

The charging port of the OnePlus 2, interestingly, is a USB Type-C port, not the standard Micro-USB slot found on most Android phones. That might sound exciting, but it lacks some features: one, it's USB 2.0, not 3.0, so lacks faster transfer; two, because it doesn't employ Qualcomm's Quick Charge technology (nor is there wireless charging); and three, because if you lose it then you're in more trouble than normal. However, the opposite standard USB end is reversible, meaning either side can plug into a port to charge; it does look cool in its red and white finery; and a full charge from a wall socket takes around two and a half hours, which is pretty quick for a 3,300mAh battery capacity.

Then there's the strange absence of NFC, despite the inclusion of an excellent fingerprint scanner on the front "home" key of the device. Having one but not the other means Android Pay is as good as useless with this phone. However, we rarely to never meet anyone who uses NFC to sync their music to a device, for example, so can see its absence from that point of view, especially considering it's an expensive technology to implement. Arguably the phone-based contactless payment world isn't in full swing just yet, but OnePlus ought to be ahead of the curve rather than chasing it.

Pocket-lintP1020126 copy

The fingerprint scanner itself is great though, as good on the OnePlus as Apple TouchID (we tested them side-by-side) or the Samsung Galaxy S6's latest implementation of the technology. You can train the OnePlus 2 to learn your finger and thumbprints, with multiple presses in the setup process mapping your digits with accuracy that results in speedy touch-and-hold login (when fingerprint access is activated anyway). As with this kind of technology, wet fingers cause issues with readability, but a backup PIN entry screen means a swift alternative access point is always there. No iris scanning or anything like that just yet, but for the money you couldn't ask for a better fingerprint scanner.

One of the features in Android Lollipop that really annoys us is how notifications are handled and how difficult it is to cease vibration without digging into the menus. Now while the OnePlus 2 runs OxygenOS 2 (more on that in a moment), it's built around Android and, therefore, has this same dig-deep-to-find-it vibration controls. Only OnePlus has been clever and included a physical three-position slide switch to the left side of the phone to jump between all/priority/no interruptions, which is an excellent way to cut away one of Android's newer irks (even if it is just a personal one of ours).

When companies invent their own re-skins – you can sort-of read that as operating systems – it tends to give us the fear. For years Samsung, Sony, LG, et al, forced excessive amounts of their own software and apps down our throats (some good, some not) that ate into storage space, only to more recently cool off and only leave the good stuff available.

READ: OnePlus 2 OxygenOS 2.0: 7 software features to check out

But OxygenOS 2.0, which is OnePlus's build upon Android Lollipop, does a fine job in the OnePlus 2 and doesn't stray too far from the stock Android norm. There are a few microsecond-long animation excesses, perhaps, such as when exiting from the list of open apps back to the home screen, but otherwise it's a slick, flagship-like operation.

Exceptions are few and far between: we've experienced no crashes or time-outs, only a few occasions when things have hung for that moment longer. We'll put that down to teething problems which, via updates, we expect to see ironed out in the near future. There's also an annoying bug with Automatic Time Zone which glitches out and randomly shifts the time (on our visit to San Francisco it's been automatically flipping between PST and a time zone three hours ahead of that).

From what we've seen there are no horrible nasties hiding within OxygenOS 2.0 either, just a handful of beneficial apps. Given its Samsung-styled physical home key and recent and back buttons to either side (their functions feel back to front by default, but can be swapped within settings), the OnePlus 2 doesn't have on-screen soft keys by default – but you can switch them on within the menus too, leaving the choice of operation up to you.

Pocket-lintOP2_screen_009

Elsewhere there are genuine benefits, such as SwiftKey Keyboard from the off, which is far superior compared to many in-house swipe-to-text and predictive equivalents. OnePlus, unlike Honor, hasn't been foolish and negated having an apps tray either, although in the OnePlus 2 the most used apps (accessed via a left swipe of the screen, a feature the company calls Shelf) may trump the long-winded method of access – we've found ourselves using that more than digging into some personally created folders.

The one oddity, which seems to mimic other Chinese makers such as Huawei, are Gesture controls. Not gesture as in three finger swipes, but instead you can draw an "O" for the camera to open, or a "V" to flick on the flashlight. When we think of flicking a V we think of something entirely different… perhaps that's why such features, while harmless, have remained unused except for grasping their existence for this review.

Such performance smoothness could be put down to that Snapdragon 810 processor, we suppose, although that's been one of those processors that's had its highs and lows in various guises. In the Sony Xperia Z3+, for example, it's awful, overheats, and murders the battery life.

The OnePlus 2 is different. The 1.8GHz processor is clocked slower than its configuration in other devices, which, in this large scale body at least, results in less noticeable heat being emitted than its nearest competitors. The Samsung Galaxy S6's Exynos processor runs hotter, for example, or comparable Sony and Huawei flagships.

And we mean that whatever is thrown at the OnePlus. Our recent addiction to just-released-for-Android Fallout Shelter has seen us constantly diving into the wasteland vaults, but even that intensive app has failed to make a dent at any moment. Everything runs smoothly and responsively, without overheating, and although it impacts on battery life it's not enough to see the OnePlus 2 bow out early in the day.

Pocket-lintP1020125 copy

Indeed the 3,300mAh battery on board is a capacious beast, full of stamina. On busy days, even with ample gaming included, we've made it through the day no problems with plenty of battery remaining. On one rather over-the-top Friday night we awoke with the phone, unplugged, at our side: it'd be alive a full 24-hours and had over 10 per cent remaining. God knows what WhatsApp messages we'd sent.

So as much as some will criticise the OnePlus 2's choice of processor and clock speed, we find it a savvy balance. We'd take longer battery life and decent performance compared to an overheating handset that can benchmark higher because the experience is better.

Part of that battery longevity may also come down to the screen. The 5.5-inch panel on board the OnePlus 2 may be large, but its 1920 x 1080 pixel (Full HD) resolution isn't stacked with extra pixels, like many flagship devices and their QHD (2560 x 1440 pixel) displays, such as the LG G4 or Samsung Galaxy S6.

You may want a flagship with the most pixels, which is fine, but you'll have to pay for it. Plus we've rarely seen most top-spec phones utilise such heady resolutions to great effect, often failing to capitalise on decent dual-window software, for example (excluding Samsung; LG's dual window software is fiddly). You don't get such double-window software in the OnePlus 2 either, but then it's playing with less pixels in what we find to be a very agreeable solution. Put it this way: the poorly performing LG G4c mid-ranger costs just £30 less than the OnePlus 2 and has less than half the resolution (1280 x 720 pixels) on its 5-inch screen – a screen with lots of other issues besides.

For the money, the OnePlus 2's screen is a class act, with ample brightness and a colour palette that feels natural and accurate rather than ready to singe your retinas with pushed saturation. It's an IPS panel with decent contrast too, offering decent angles of view, so no contrast fall-off to be found here. It's all held within trim bezel and encased in Corning Gorilla Glass for added style and protection.

With the OnePlus One the hardware choices meant limited 4G availability in the UK, depending on network provider. Not so the OnePlus 2, which we've been happily using with 4G (shown as LTE) over the past week on Three network.

Pocket-lintP1020136 copy

Signal with Three we find to be generally poor in our area of London, so it's hard to make a judgement call as to whether the OnePlus 2's antenna suffers greater problems with reception than other handsets. When out in the open we've made a bunch of calls and everything has sounded clear and crisp with no drop-outs to calls.

Which brings us on to sound, as there's the addition of MaxxAudio Audio Tuner, a full-on equaliser with 10 band adjustment. Additional enhancements can boost bass, treble and dialogue, while three presets – music, movie and game; each of which saves settings individually – means it's ultra simple to swipe to a preferred preset depending on what you're watching or playing. And considering the speakers are only dinky milled openings to the base of the phone, that audio sounds rather impressive overall.

Any flagship worth its salt these days has a camera with performance to rival a dedicated compact. The OnePlus 2's isn't quite as strong in terms of operation compared to the high-flyers – the Samsung Galaxy S6 is really something – but it does a sterling job when it comes to image quality.

To the rear is the main 13-megapixel camera, the lens of which sits almost flush to the phone body for a tidy appearance. None of the considerable protruding lens nonsense here, just the thickness of the metal surround. The lens itself has a bright f/2.0 aperture to let lots of light in, while optical image stabilisation helps to keep those shots steady from the likes of handshake.

Pocket-lintIMG_20150817_122822

There's no dedicated shutter button which is a shame (it's an on-screen virtual button instead), but controls are otherwise simple: use the touchscreen to press for focus, which is swift thanks to laser autofocus, whereafter the circular focus point will remain, providing the opportunity to drag an exposure compensation circular slider up or down. Thing is, the exposure level continues to adapt to changing lighting conditions rather than locking, so sometimes the manual adjustment made doesn't seem to adjust on screen at all.

This exposure adjustment is the only manual intervention available too, making the OnePlus 2 a point-and-shoot style camera, so if you're looking for manual ISO, shutter speed and aperture controls then you'll want to look elsewhere. Not a deal breaker for most, we'd imagine.

Some additional photo modes are also available: HDR (high dynamic range) for balancing shadow and highlight detail; Beauty, which softens areas of the face for a supposedly "beautified" result, possibly (not) ideal for use with the 5-megapixel front camera; and Clear Image, which stitches together 10 photos for a super-high-res file which only takes a couple of seconds to process. On the video front there's 4K capture available, which is becoming more standard, or you can shoot slow-mo or time lapse too.

The base sensor in the OnePlus two is the same as found in the Samsung Galaxy S6 so, as you can imagine, the results are quality. Whether you're shooting in sunlight or moonlight, it's the OnePlus 2's resulting images that see it shine. The getting there part could be a preened a little more though.

Verdict

The OnePlus 2 is an exceptional phone, without just taking the price into consideration. Yet the fact it's less than half the price of most flagship devices is what really impresses.

However, there are some niggles: no microSD card storage; the absence of NFC when there's a decent fingerprint scanner on board is just illogical; and the actual process of buying one, via invite, is a pain in the behind. But it's that last point that almost gives the OnePlus 2 added allure, garnering it even more worthy attention.

Really the OnePlus 2 lives in its own space, because nothing else at this price point delivers nearly as much. It's single-handedly demolished the mid-range market, and while it lacks some elements of flagship finery such as a QHD screen resolution or NFC, we've not missed such features during our week of use.

And that one week will turn into many more; using the OnePlus 2 has made us realise that we won't be swapping back into the LG G4. And while we would still opt for a Samsung Galaxy S6 edge if money was no object, the OnePlus 2 is the antithesis to that concept. If only it was easier to actually buy one.