I fitted a nest as part of a full central heating replacement. Therefore i'll keep my review short as I sorta wish I was able to compare the old to the new!
The box comes with the thermostat, optional back plate, hub (to fit in your system) and the required cables. the hub was easy to fit, and is essentially a replacement for the HW and CH control for your system. this is most commonly found near the boiler however my plumber fit this near the hot water tank as it was specific to the system I was having. Once the hub is on, its as simple as turning on the nest, installing the app and your good to go!
I fit the nest without the back plate, as I think it looks sleeker. Word of warning that the nest thermostat requires constant power to operate, and this comes from a USB cable. If your looking for a sleek fit, then I chased the USB cable into the wall and plastered over it.
Once running, the Nest works perfectly. Its actually surprising how natural it is to change heating and water schedules using the app. I cant believe we were slaves to our previous schedule purely because the old control was so fiddly.
The Nest app also works particularly well to recognise when your away from home, and adjust your heating accordingly.