I took the wall thermostat to where intend to put the range extender, and it worked, so don't foresee any problems. Worst room in the house, faces Northwest, has two windows, and above the dinning room which is hardly used in the Winter. My hope is, if that room is warm, then the boiler running long enough to ensure all rooms are warm enough to turn off the TRV head in their room.
I made a miscalculation when I installed the first thermostat, wires went to the hall, were sticking out of the wall, so assumed the thermostat had been in the hall, found the receiver,
but no thermostat, the one under the receiver was for flat under house, not main house. There was a programmer
but found only 2 wires of the triple and earth had continuity, and also changed from red, yellow, blue, to brown, black, grey, so somewhere there must be a joint. So seemed prudent to use extra low voltage, so installed Nest Gen 3. However, it seems the hall is the slowest room in the house to cool, never considered cooling speed, heating speed you can adjust with lock shield valve, but cooling speed nothing one can do.
Living room has a wood burning open grate, and patio doors, so not really where the wall thermostat should be, but as a second thermostat in parallel with Nest even if batteries go flat, still get some heat, so fitted Wiser in Living room, tried it in different places, but for some reason cat decided it would sleep on the thermostat, so had to wall mount.
My bedroom got warmer as well as living room, but wife's room gets rather cold, I was careful to put her unit on legs, so through draft around radiator, but then set drops stuff on the floor, but if the TRV head reports the room is warm enough, I can tell her heating OK, stop blocking air ways to radiator.
So crossing my fingers, that this will remove the ear ache, and she will stop complaining. If I can say "Hey, google what temperature is Linda's bedroom." and it reports over 20ºC, then she can't complain. It is replacing an eQ-3 head, which only told you temperature set, not current temperature, and only work with one phone, so fingers crossed, I can now blame her if room too cold.
Did test and Nest Mini speakers will report temperature set and current temperature and will adjust temperature with a voice command. She does not even have to get he phone out.
Battery full, No Signal 
It seems Zigbee, and each device relays to next, I have Zigbee elsewhere in the house, but does not seem to be connected to Wiser.