If you install underfloor heating with a heat pump, then the towel radiator, if you really want it, only with electricity. Under no circumstances use ones connected to the heating circuit.
You then have a metal radiator in a plastic circuit that dirties your entire system. In addition, you need a high flow temperature for radiators, but the heat pump should deliver as low a flow temperature as possible. If you want additional heating in the bathroom, use a wall heating system or infrared mirror heating.