Number of points:-
1) Is the "Blue in connector block" a neutral, if not, then a non-starter.
2) "Just to control room temp" would an electronic TRV heat not do a better job?
the standard picture of air movement within the room shows the most likely place to monitor the whole room air temperature is on the floor just in front of the radiator, the TRV is so close to the ideal position to be neither here nor there.
I can see how we like to see a thermostat with looks modern and in keeping, but the main thing is it needs to be where it has a reasonable average for the room. In my twin radiator L shaped living room, three walls are non-starters as outside walls, by the open fire is clearly not a good position, so I only have one place it could go, where there is no wiring to connect it to. So either it has to be wireless, or I use the TRV heads.
For the whole house, I also need to control DHW, likely the hall is the best location, and is where the wiring goes, however I have found the hall cools slower than the living room, but since an open fire in the living room that is not a good location for a single thermostat.
So I have got around the problem by fitting two wall thermostats wired in parallel, to ensure the boiler runs if either hall or living room is cold, over heating is stopped by the TRV heads. But the living room wall thermostat, I have no option but to use wireless, since two if either has discharged batteries not a problem, but to get location right to control room, no option but use wireless.
In the main, to up-grade the controls, forces the use of wireless, be this the TRV head to hub, or wall thermostat to hub. Wireless can be good, mine came with a stand and I tried various locations before settling with the one I have now, found using as freestanding did not work, darn cat decided to sleep on it.
I will likely add to the system, using linked TRV heads, if any need replacing. Heatmiser then to be for underfloor heating, with sensors in the floor etc, may be better if you say what your aim is.
