The Hive Radiator Value is a connected thermostatic radiator valve (TRV), allowing you to swap the head of the manual (or disconnected) TRV on your radiator and link it into the Hive system.
That will allow you to set precise temperatures in individual rooms - meaning that you don't have to heat a room you don't use, or can choose to have lower or higher temperatures in different rooms depending on your preference.
The advantage of adding them to a Hive Active Heating system, however, is a more integrated heating system where you'll be able to, for example, turn up a radiator in an individual room without heating the other rooms in the house - ideal if you have a home office or similar.
In many cases you'll be able to install the Hive Radiator Values yourself by following the instructions in the app - often it will just involve unscrewing an existing TRV and putting the Hive unit on in its place. Those with older systems might need to consult a plumber - and if you don't have TRVs on your system already you might need to have the values changed to accept the Hive units.
The Hive Radiator Valves will be available in packs of one, three or five, priced at £54, £139 and £199 respectively.