Very good.
Very low.
Depends on how handy you are...it is not that difficult if you are reasonably handy, but do your research first, as it is very difficult (as you might imagine) to tweak/fix once you have installed your floor.
Big difference. Warm feets = warm you, and since the heat radiates upwards from a broad base, it warms the air nicely, too, so your furnace will not be on as much. It is very efficient, and due to its nature, does not dry the air or create/move around dust the way a forced-air furnace does.
I know a number of people with this sort of heating in one or more rooms of their home, and not a single one regrets installing it.....it is particularly nice under the bathroom tiles, and in the kitchen.