Tado smart thermostat without central thermostat/controller

Not sure if you've gone down this route or not?

My previous setup was as you describe (TRVs on each radiator) - but I also has the smart thermostat and extension kit. When I messaged Tado about this point - they said they could programme it for the extension to fire up the Boiler whenever a TRV called for heat.

I'm only ran it for around 3 months, as our house has now been gutted - but have re-set this up with our new boiler.

My experience was more comfort and the ability to heat individual rooms and remotely switch things on and off (have a largish 4 bed house, with 2 adults and 2 kids) - but fairly sure we probably save 50% of our usage by only heating when we need it (on a room-by-room basis).

I think the whole system was something like £800 (14 radiators) - so hoping to achieve payback in 4-5 years maybe... (£200 a year).