The thing is this is your heating system running at full capacity because the entire heating loop is balanced for that to be all on. If however you're only using 2 rads, even though the flow return temp might be quite high, the power needed from the boiler is much less because much less heat has...
We went Tado because at the time they were the only ones doing connected TRVs. I note Hive are now doing them.
The great thing about this is you can effectively programme every radiator in the house so that you can use them individually. I have been able to programme my son's to his college...