I had stopped in a house with under floor heating in the bath room and it was great. Clearly the guy installing knew what he was doing. So when my mother lost her leg and we wanted to install a wet room we stipulated under floor heating. It was a failure but not all down to it being under floor heating so I will list them for the reader to decide.
*) Original install damaged by builder requiring lift and relay.
*) Idea was floor would dry quickly but once wet from shower it cooled down to much and recovery time too long. Add that sculptured tiles were fitted to give more grip which held the water longer it took 1/2 hour for floor to dry by which time Mum long gone.
*) Set to maximum temperature where one could walk on the tiles without also having a towel rail on the room was cold. The extractor would need changing for heat recovery unit if it was sole heating method.
*) The thermostat only lasted about a year each.
*) When the floor sensor failed it got stuck in the pocket.
I have looked at other systems one local one shown here.
The main point is it was built like that in the first place and not an add on.
There are systems today
this is designed to under heat a seat but could be adapted to under floor. The main idea is to store heat so there is a large quantity of stone to heat up. So for a retired couple likely will work well running 24/7. However the idea of only heating the house when home will not work. It needs to be used like storage radiators to work.
Pictures are also links.