I have heard it said that in floor heat, and especially in slab heat doesn't cycle temps very well at all, precisely because of the big delay. But if you just pick a temp and leave it, then they work well.
I don't notice that big a difference when we put radiant in the kitchen, for me it was a way to put a door where one baseboard was under a window, and a fridge and cabinet where the other baseboard was. I do think the heat is more even than the baseboards since by design it runs longer at lower temperatures and isn't cycling as much. It did require a mixing valve added to the furnace to keep the cold return water from shocking the hot water for the other loops. I gather that doing all radiant would be both simpler on the mechanical side (retrofitting the rest of the floors would be a pain however) and more efficient, since the boiler would only have to provide water at one temp.
My wife says she definitely notices not having cold feet anymore, and aging lab is often on the only padded surface in the kitchen, the mat by the back door. I keep checking if she's there because she wants to go out, like in summer, but she's there because she's comfy (there's a dog door). The Aussie with his heavy coat is never on it, always picks the coldest surface inside or out.
