Sotal, these small heat pump/AC units are as cheap as chips & they have a COP of 3-4, but when trying to heat your conservatory with -10*C outside temperatures they are useless, and you would be better with Telly Tony's £9.99 fan heater. However, for the most of the year they're great.
UFH is a radiant heat, so the heat will always go to a cold surface(ie Glass), so unless you have good U values in the fabric of your construction, it's unfortunately a waste of time. UFH is one of the best forms of heating, if you lived in a house with it installed, you'd agree.
The HP/AC units are cheap, easy to install & quite cheap to run. However, it's blow heat, as soon as the unit goes off, you are cold, unlike a radiator or UFH.