Myself and a buddy put these in just over a year ago and they've been going strong. If you have leather you'll probably have to use high heat most of the time but with cloth.....it really starts to cook! Install was pretty easy, leather a little more difficult just because its a little less forgiving.
I put these in my Gf's cloth seat Fiesta. The install was a little bit of a pain but in the end they have worked great over 2 winters. My only thing is most of the kits just have you zip tie your seat back on vs using hogrings. I would recomend the hogring method but that is just my opinion. Hogring pliers also help a lot.