I do have electronic TRV heads,
5 x eQ-3 bluetooth only, programmable, so rooms only heated when required, but bluetooth will only work with one phone, and have to be close to it.
3 x Energenie should work with Nest, but don't, they can't be manually set, so in many ways the eQ-3 are better, but does show current and well as target, the eQ-3 only shows target, they connect to a hub which in turn connects to internet.
1 x Kasa, can be manually set at the unit, but eats batteries, should work with a wall thermostat, but the wall thermostat like the Energenie has to be hard-wired, so just connects to the hub and internet like the Energenie, does give more info as to what the room has done, but non have what I would call intelligent functions.
The last is Drayton Wiser, this is the only one which can fire the boiler, as with the Kasa it gives charts showing how it has done, however the way the plumbing has been done, does not help, the radiators are on outside walls, this means cold weather cools the TRV before it has cooled the room, so when the heating is still not running the set temperature needs to be lower to compensate for being close to outside wall, but when the heating is running the thermals generated means it needs to be set higher.
The others have the same problem, but they don't fire the boiler, so set at running temperature is OK, so all this working out when to switch on to get room to temperature on time, is a bit pointless, as have to manually change the temperatures or boiler runs when not needed.
With mother's house all radiators were on internal walls, this means the TRV worked spot on, but the wall thermostat was colder than it should have been, so if radiator on outside wall then need wall thermostats, and if inside wall then TRV's, but there is no device easy fitted to work the TRV from a remote sensor.
Also, TRV's do not move around the house, they stay fixed to the radiator, so why can't you get mains powered versions? Fitting 20 x AA batteries every Autumn is a pain, and worried about batteries leaking, and not really good for the environment to use batteries, OK, in some locations I would have a problem as retro-fit getting power to them, so some would need to be battery powered, but there is no option to fit either, mains powered or versions with remote sensors, which still connect to same hub as the battery powered versions.
I like the way my Nest Gen 3 shows me as I walk past what the room temperature is, I need to manually press a button on the Wiser wall thermostat or use the app, and also like I can read Nest with my PC without an emulator, just a pity Nest is such a useless thermostat. And useless information given, it says Energy History on the app, but all it shows is when Nest called for the boiler to run. OK my boiler simply on/off, but most boilers modulate, so run time tells you nothing, and my boiler has two hubs and a thermostat which can all fire it up, so run time for one wall thermostat is useless.
What would likely help is run time for DHW, I had it drummed into me that gas is cheaper than electric, don't use the immersion heater, I assumed oil was the same, but my system does not have a tank thermostat for the oil so to work out what used, run time of the boiler, since it does not modulate, so 20 kW boiler and by experiment we found it would only run for around 20 minutes before boilers internal thermostat turned it off, and having 4 x ½ hour slots per week gave use warm water in the summer, little worried about legionnaires but never got around to finding a wireless thermostat, which if I had would have cost more to run.
The problem of using a boiler, be it for a railway engine or central heating, is the cost of the match, i.e. what it costs to heat the boiler before you get any useful work from it. We have energy to heat the boiler, and any pipe work between boiler and holding tank, before anything comes out of the taps.
So to heat DHW with oil, used around 30 kWh per week, and the iboost+ tells me with electric at a higher temperature so no worry about legionnaires, it uses 12 kWh per week, it cost 15p/kWh in lost revenue as not exporting it, which is about double the cost of oil, but the losses as so much reduced, this time of year I would be thinking of topping up oil, would be around 1/3 full, using an immersion it is around 3/4 full, that is a lot of oil, does not take much intelligence to work out, using electric is cheaper to using oil.
As to combi-boilers, son changed the main 7 instant gas boiler and central heating boiler for a combination type, with old boiler run a bowl of water, and started cold then got hot, so net result water right temperature to wash dishes, now one has to run half a bowl of cold water away to get a full bowl of water to wash dishes, that's a lot of wasted water, and likely a lot of wasted heat, the boiler heats a small amount of water which with a heat exchanger heats the DHW, where the old boiler heated DHW direct, and this waste is every time one wants DHW, maybe 20 times a day, that is one heck of a waste of energy.