Re Fan Coil Units, when we fitted ours 7 years ago, Panasonic called it an Air Rad. We went for it to provide spot heating/cooling in the main (and only) upstairs bedroom. What they didn't tell us was that, in heating mode, the valve in the unit is thermostatic and will only open when the water reaches a particular temperature (circa 50C iirc). Of course, with the ASHP running UFH for the rest of the house, the water never reaches that threshold. It works absolutely fine for cooling, but we ended up adding a small flat panel electric radiator for the odd occasion we need to heat the room.
No idea if this is something that has been solved in more recent FCUs, but worth checking specs before purchasing.