The problem is working out what a system will really do. The BBC linked to
this web site claimed to compare heating systems, however I have Nest Gen 3 wall thermostat and Energenie TRV's and I can say they don't really work together. The Energenie app will change both together, but any schedule change is not relayed to the TRV, and it works wrong way around anyway, want TRV to tell wall thermostat not wall thermostat tell the TRV.
So we have:-
Hive likely a good one for you as you don't need the OpenTherm and that is the main down side, but also will not take a demand for heat if the wall thermostat is over 22ºC not sure if that is good or bad?
Nest is only any good when you don't want linked TRV's
Honeywell Evohome likely one of the first but still works well, plus point is can be controlled from the wall thermostat, no need for apps on the phone.
Drayton Wiser is claimed to have algorithms built into the TRV heads so it works out when to stop heating the room so as not to over shoot, important if using geofencing, the anti-hysteresis software on my Energenie is OTT so to heat the room to 20ºC I have to set to 22ºC for an hour then back down to 20ºC or it would take 3 hours to reach temperature.
Tado seem not to want to release information about their system, read good reports, but question why they will not tell you what they can do.
The USA Nest uses temperature sensors, so you monitor say 4 rooms, and if any room under temperature the furnace (their name for boiler) will fire up, there is nothing to stop us fitting multi wall thermostats, I did it with mothers house, wind direction would change which rooms heated up first, so used two thermostats in parallel either end of the house. This house the problem is routing the wires.
Many people seem to be using the
Moes thermostat there are three versions so need to be careful to select correct one, but much cheaper than other wifi linked thermostats, not a clue how well they work.
But at end of the day the non modulating thermostat is simply a switch, there are basic two types, 230 volt and volt free contacts, the Salus you show
is sold under many labels, they are known for loosing wireless link, and they do not fail safe, so when they loose the link the heating can stick on, reading the manuals both need a link wire if switching 230 volt, so basic what is in one will go in the other, but I don't know if you are switching 24 volt or 230 volt so don't know if either has a link wire.
The advantage with the Salus was you can move the sensor around, with TRV's set not to over heat the rooms, it was a simple thing to move the sensor room to room, and until the unit failed it did work well. I fitted unlinked TRV electronic programmable heads, in that house Energenie, but in this house also use eQ-3 heads which cost £15 each in 2019, the Terrier i30 can do the same, I found the cheaper heads work better, mainly as I don't walk around glued to my phone, so walking up to the radiator and pressing the eco/comfort button as I come to use a room is easier than opening an app on my phone. The bluetooth version of eQ-3 can be controlled with one phone, can't set it up to use two phones, and if two radiators in one room the TRV's can be linked.
If you do fit Tado please report back, the Drayton Wiser seems to get very good reports, the Hive when one asks it seems very few people also fit the linked TRV heads, and no one seems to sing their praises who have fitted TRV heads.
If I was reading that report linked above Nest Gen 3 seems very good, however having fitted one, would not recommend it, I have had to switch off nearly every smart feature.
Geofencing with Nest does not allow you to set the distance, only comfort and eco temperature, however if it detects movement in front of the thermostat it will turn up the heating even if phones not shown as being at home. Some geofencing allows one to set the distance.
