I've got some in our garage, it's being put down next week on top of electric under floor heating. We need radiators too as we aren't allowed double glazing & the ceilings are v high AND we have loads of windows (listed property). I'm hoping it will look good.
We used a water based system than connects to our gas boiler and the rest of the house system. There is absolutely no need for radiators in the same place.
The boiler pumps out 70c water to the rest of the house (upstairs) radiators on the timer. There is a separate valve and timer circuit from the boiler to the kitchen/dining room UFH. The 70c water goes to a manifold that mixes the temp of the water with cold down to 35c. The whole floor heats up to about 25-30c and the heat permeates everything in the room.
The UFH stays on 24/7 from the late autumn to the late spring. It's much cheaper to run it constantly as it takes several hours to heat up and cool down, plus the energy demanded is much less. My gas bills went down after we installed it.
Our installation has 5cm of insulation board (Kingspan) underneath, on which the pipes are laid and then a 5cm layer of screed (soft concrete) is set and the tiles go on top. The tiler needs to take care not to dot and dab leaving air gaps between the screed and the tiles as the heat won't rise through those air gaps - there needs to be grout under 100% of the tiles so they're in direct contact with the heated screed.
Make sure the pipes are continuous runs of high quality polypipe. I've heard of people putting in copper pipes with corner joints. A recipe for a leak in my opinion.
I went to the Home Improvement show at Olympia recently and saw new water based systems that use much slimmer profiles so you might not need the 10cm depth we did (10 years ago).
These are the guys who designed and supplied the system to me. I got the plumber and builder to install it, but you need to make sure they follow the comprehensive installation instructions as, often, they think they know what they're doing, but don't and take silly shortcuts.
I've been looking at stone for kitchen flooring. I think it looks wonderful. The one I like is £100m2 which seems very high. I understand you have to have it sealed, not sure what that involves? Someone told me it scratches easily. Apparently it doesn't sure the dirt, which is a big bonus.