It's September, the kids have gone back to school, Starbucks has started selling Pumpkin Spice Lattes, and Apple has released two new iPhones: the iPhone 6S Plus being the larger 5.5-inch screen device than the standard 4.7-inch 6S. But with this being an S year, rather than a fully next-generation model year, is it worth getting excited?

Like the iPhone 6S, the iPhone 6S Plus remains almost identical in terms of physical form to its predecessor from last year. But at the heart of the new device are new features and new ways to interact using 3D Touch.

READ: iPhone 6S review

The iPhone 6 Plus was a huge success for Apple (huge being the operative word), so does the new model continue that pattern, challenge its large-scale Android competitors, or does the more compact 6S make better sense? We've been using the new iPhone 6S Plus for a number of weeks since Apple's Special Event to see whether it's a step ahead.

While on the surface the new 6S Plus looks identical to the original 6 Plus, and both have the same 5.5-inch (1920 x 1080 resolution) screen, there is a slight change in the dimensions and weight.

The iPhone 6S Plus measures 158.2mm x 77.9mm x 7.3mm and weighs 192g, compared to the older iPhone 6 Plus's 158.1mm x 77.8mm x 7.1mm and 172g. In reality though, unless you are some kind of savant, you aren't going to spot those minute expansions.

However, you will feel the difference in weight. Although not confirmed by Apple, it seems adding 3D Touch (more on that in a moment) and using a tougher aluminium for the chassis has taken its toll, hence the 6S Plus gaining 20g. In real terms that's the equivalent of carrying 20 £1 coins in your pocket, making it £2 heavier (in terms of weight) than the earlier model. There's no doubt that the iPhone 6S Plus is a big beast.

In terms of colour options there's Silver, Space Grey, Gold and Rose Gold, with the final two in that list exclusive to the S range of phones (no Gold option for the earlier iPhone 6 Plus any more). If you really want to send a statement then go for the Rose Gold one - it's very pink.

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One of the biggest changes to how you use the iPhone 6S Plus is the introduction of a new feature called 3D Touch. Put simply the phone now knows how much pressure you are applying to the screen, which can be used to access additional options - much like the way Force Touch on the Apple Watch and the MacBook trackpad works.

Press on an icon on the homescreen, for example, and a new secondary menu appears giving you shortcuts, or Quick Actions as Apple calls them. All the major Apple apps support the feature, from Mail to Contacts, with the promise of third-party support in the future. 

It would be easy to brush this new feature aside as a gimmick, but it is far from it. The actions, which span across all facets of iOS 9 (more on that latest operating system update later), are designed to speed up tasks that previously took two or three taps of the screen. It's a small change, but it all helps speed up that journey.

It's not just about shortcuts on your favourite icons, though, with Peek and Pop acting is another element of the 3D Touch overlay. As its name suggests this allows you to peek into emails, web pages, photos or messages to see what's going on, then if you like what you see you can "pop" into the app in full without having to come out of what you were doing and load the specific app separately. Again, it's all about speeding up your processes and power users are going to love it.

Other apps like Notes and Mail (now with Markup) use the tech for determining the pressure of a pen, useful for a more precise handwriting experience. You can adjust the level of pressure you need to apply to make the feature work - something we've found ourselves doing. It gives the 6S Plus's large screen real estate a new breath of life.

The only downside, so to speak, is that it will take some time to learn this new interactive approach. Not because it's hard to use, but because you'll forget these options at first as your learn what's possible. But once you've got it, you'll be, ahem, hard pressed to go back to how things once were.

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One of the main reasons to go for the 6S Plus is the fantastic camera. Featuring a new 12-megapixel sensor and, perhaps more importantly, optical image stabilisation for both stills and video (which lacks in the smaller 6S model), the 6S Plus really is a convincing compact camera replacement through and through.

Photos are natural in their colours and tones. Like the iPhone 6S we're impressed with the autofocus too - it actually focuses on the subject, rather than trying to make the whole scene sharp - and copes well with an array of lighting scenarios. Whether that's shooting stills in low-light or sunlight we've never struggled to end up with good-looking results.

The optical image stabilisation really works its magic as well, stopping images from falling into that blurry smartphone territory which is all too common.

On the front the 6S has a 5-megapixel iSight camera, but most important is a new feature that turns the entire phone screen into a sort-of flash for those perfect selfies. Press the shutter button and the phone will analyse the light needed and then change the hue of the white accordingly. We've seen bright clean whites through to creamy tones depending on the ambient light situation. Even in pitch black situations this flash is good enough to deliver a useable photo, albeit a noisy one.

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According to Apple, the problem with still photos is that they don't show what's happening at the time you take the photo. That laugh seconds before or after a magic moment, or the movement in the background of a river or waterfall. Its answer is something it calls Live Photos, which work by taking 1.5 seconds of video (including audio) before and after the shot to give you an added sense of movement.

Thing is, it's not exactly a brand new feature in the tech world. Look back to Cinemagraph from Nokia, or HTC Zoe, and you'll find similar solutions (ones that aren't talked about much at all these days).

So far the people we've shown Live Photos to have fallen into two camps: those with kids and those without. Parents automatically seem to get it and love it. Others, at the moment, not so much.

The iPhone 6S and the 6S Plus are the only two Apple phones that can capture these Live Photos, but it's possible to share them with other iOS 9 and Mac OS X El Capitan users and keep the effect in place. But sending to Android and friends on other platforms won't work - they'll just receive a default still photo instead.

Apple tells us that Live Photos will get even better with an upcoming software update that will intelligently sense when you raise or lower the iPhone 6S, so that automatic capture will take place at the pinnacle moment. We can definitely see the need for that, as a lot of Live Photos we've shot have footage of us hastily dropping the camera after taking the shot. Another frustration is that audio is automatically recorded, which at times is lovely - a child's giggle for example - but not so great when you've got the same child screaming in the background.

All that extra video adds to their size too, meaning a Live Photo in is worth around two still photos in terms of space. While you can offload some of that to Apple's iCloud Drive service (at a yearly subscription) a 16GB iPhone 6S Plus isn't going to stretch as far as it used to (compounding the argument for a 32GB minimum model).

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The iPhone 6S Plus also adds 4K video recording (3840 x 2160 resolution) at 30fps, alongside optical image stabilisation for video - the latter feature not available on the iPhone 6S.

4K video performance is great, although only if you've got a television or monitor with high enough resolution to playback at its fullest resolution. You'll only ever be able to view it as 1080p on the 6S Plus's screen itself or if you stream it to your TV via an Apple TV (the new one isn't 4K compatible either).

That's probably why the 4K option isn't on by default and why Apple has hidden it in the Settings app, rather than being accessible via the Camera app itself. At least you can edit 4K on the device with the help of iMovie, although be prepared for the phone to get hot and eat into battery life if you do.

If you have got somewhere to play the content in native resolution then you aren't going to be disappointed with the performance. The 4K footage we've shot is stunning, and failing a high-resolution screen to play it back on you can always use the extra resolution to zoom in to enjoy the new detail you've captured.

If you're looking for slow-motion options then 1080p is available at 120fps for up to quarter speed smooth playback, while 720p at 240fps means smooth playback at up to one eighth speed. No 4K slow-mo options are available.

With a new iPhone comes a new version of iOS, and this year is no different. Apple has introduced iOS 9, complete with a number of new features and enhancements to make the phone not only work more efficiently under the hood, but also to make day-to-day use easier than ever.

READ: iOS 9 review: New and innovative or more of the same?

Those paying close attention will notice a newly designed font (Apple's in-house one created San Francisco) which features wider spacing (kerning), a new app switcher that benefits from the bigger screen on the iPhone 6S Plus and greater focus on search via Spotlight and Siri. The 6S Plus doesn't get the iPad multitasking elements, however, but it does enjoy an abundance of keyboard shortcuts and a landscape app layout.

When it comes to battery life, the iPhone 6S Plus is still incredibly impressive, delivering more than a day's battery from a single charge. Add in the new Low Power Mode and you can really extend that a lot further than you've been able to do before with an iPhone. Taking cues from other companies like Sony, this mode can be turned on at any point and actively reduces certain features like Mail fetch and background app updates to preserve battery.

It's perhaps not as necessary in the Plus as it is with the standard 6S, after all we've struggled to drain our earlier 6 Plus battery in a single day, but it's good to know it's there if you need it. You are prompted to activate it at 20 per cent and 10 per cent battery level warnings, but the system never automatically turns the mode on without your approval - an unusual decision, given Apple's choice to proactively help you elsewhere in the OS. 

In our ad hoc tests in the office the iPhone 6S Plus was able to run for around 24 hours using only 29 per cent of its battery. That's going to be great for weekends away, or those moments when you've forgotten your charger. So long as you don't go too heavy on the gaming, as that will inevitably eat into life.

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Like the 6S, the Plus also enjoys a performance boost compared to last year's model. The new A9 processor - said to deliver a 70 per cent CPU and 90 per cent GPU bump - now has the M9 motion processor on board. By integrating the two you get Hey Siri voice commands and better activity tracking, although we don't expect many to be keen to take the 6S Plus on a run - we tried and couldn't find any pockets large enough for this giant iPhone.

If you want the large 5.5-inch screen for gaming then the move to this latest A9 processor means a significant GPU boost. Load up Asphalt 8 or another high-end 3D game and the 6S Plus really shines. Operation is slick throughout, and we've not noticed any lag, stutter or latency issues.

Touch ID fans will also be pleased to hear the sensor has been upgraded too: it's a lot quicker to respond, although Apple still hasn't been able to solve the issue of not being able to use it with sweaty hands after running or wet tips after getting caught in the rain.

Pretty much everything seems to have been tuned to be faster, including Wi-Fi (802.11ac with MIMO) and LTE connectivity.

Verdict

Just like the original, the iPhone 6S Plus is the big-scale Apple phone for the kind of user who uses two hands and isn't bothered about the weight or space needed to fit one into their pocket.

Although most S upgrades bring minor tweaks, the iPhone 6S Plus sees notable advantages from 3D Touch. Whether that's to write on that large screen, or by hard-pressing to interact with iOS 9 in a slicker and quicker fashion than before, it's the S model to buck the annual trend.

There's even greater pay-off in other areas for going bigger: you'll get a lovely large, almost tablet-like screen (although it's still not flagship-matching qHD resolution); a fantastic camera with optical image stabilisation (which the standard 6S lacks); and a battery life that will last you well beyond a day. 

For some, though, those same factors will be negated by the sheer scale of the device. The iPhone 6S Plus is a lovely smartphone, but it's also a big and heavy one.