Had the underfloor heating on for about a week now. Comfortable living 24/7. I'd recommend this kind of heating every time.
Not really that cold for me yet but in the far north it's already far below zero; minus twenty or colder.
Underfloor heating used to be very expensive to run, and was often not used because of the cost. I knew a man who built his own bungalow and installed underfloor electric heating but he put a protective plastic sheet under the heating and up into the wall cavities that retained the heat from escaping downwards and sidewards. His running costs were minimal and I have always wondered why this isn't standard practice
I suspect it's still expensive to install even though the running costs are much lower than other heating systems. Maybe one day it'll be standard on UK new builds just like double-glazing.
If you're in an old house, it's a pain to install though. You'd have to empty everything then move out before you even start. You'd either have to take up the floorboards or a add a concrete floor to hold the heating system. We're lucky in that we've got a wet system that was installed during the building phase.
If I ever buy a home, I'd definitely be checking that I could easily install underfloor heating. Once you've had it, it's very hard to go back to other heating systems. It's the best in terms of running costs and comfort. No cold spots and no waiting for radiators to heat up.