Not sure how you come to that conclusion. Nest has so many flaws, I guess it's OK for basic use but there is some really poor functionality built in.
Honeywell T6R-HW is definitely a better choice, but I guess looks less swanky. Evohome is probably the best out the lot
I for a long time thought Evo Home as the best, however have seen been told it does not work very well with OpenTherm? I have looked at Tado as well, the major problem with them all is a lack of information.
If one starts at the room and works back to boiler, in the room the fan assisted radiator must be the best, if the slight noise is not a problem, it keeps whole room at an even temperature (not sure if that is good or bad) and as long as the air can flow having a chair in front of it does not matter much, it is small and contains very little water, so fast warm up times, there was a problem with single glazing as it blows the air around so the windows lose more heat, but main point is it does not use a TRV the water flow is not altered, so no by-pass valve required. Temperature control is with the air drawn in with a number of fan speeds. In the kitchen these are very good as can be mounted inside the kick space for cupboards. However how to use the info from the iVector Myson to control the boilers modulating I do not know.
Looking at a standard radiator, still the less water it contains the better, as the less water it contains the quicker it can react to changes in demand. However they take much longer to heat a room, and are far more likely to over shoot, never the less the closer the monitoring device is to the heat source the quicker it can react, so on the supply pipe is idea as long as some compensation is included to allow for direct heat from radiator.
Now we come to the problem, how to tell the boiler what the radiators need. Simple way is the temperature of return water, does not matter which type of radiator be it because the fan is not running or the by-pass valve has lifted as the rooms are satisfied so return water temperature increases. This works well in heart of winter, but as warmer days arrive the boiler reaches a point where it can't turn down any more. At this point it starts to cycle off/on.
So we look at the wall thermostat, this may gather info from the TRV's or simply be placed in coolest room, but its job is to stop the boiler cycling, historically wise years ago it may have been main control, but today with modulating boilers its role has changed. There are exceptions, oil boilers do not modulate very well, and open plan houses can work from a single centrally placed thermostat, but in the main the wall thermostat is only there to turn off boiler in the summer.
So big question, do you really need an automated system to turn off heating in the summer? or will manual operation be better?
So looking at controls, we have thermostatic radiator valve heads or fan speed, controlling every room, so where does a wall thermostat fit into that on a day to day basis? It can only work either if very simple i.e. off/on with no anti hysteresis software or predictive software, or it connects with the radiator thermostat in some way.
Hive does not connect to TRV heads so is only suitable really for hot air systems as used in USA, Nest has limited connection, and EvoHome and Tado do it better. As to if worth the expense that's another question.
I personally would love an answer, I have every intention of installing a kick space fan assisted radiator to kitchen, however too expensive for other rooms, using a heat store with oil central heating would help, but as to if worth the expense not so sure. The debate can go on for years, however only you can decide how far to go.
