They are electric. Sometimes, if it's really cold, I flick these on (along with the electric seats) when I first start the car as they start to waft warm air sooner than the car heater.
They're not very powerful though, so it probably doesn't make as much difference as I'd like.
What Ari said. To add on the SLC/K the headrests are adjustable so there's a reasonable chance of getting a warm neck or ears. Stuff dumped behind the seats (eg atlas) can cause issues (as I found out - can disconnect stuff IIRC)
Got them in my GTC, they're OK but in this weather, with a big coat on etc you can't really feel the benefit as your neck is already covered. Can see them being handy on a cool spring or Autumn evening though.
That makes sense - the car I am getting has the heated seats too - so hopefully its all covered for cold weather conditions. I guess if its that bad you just leave the roof up!