I usually install 5-7 full leather kits a month at work, and most of them want seat heaters in the two fromt seats. These are the ONLY seat heaters i use, they have a high/low setting on both of them and have thermostats built into the bottom pad to ensure they dont get to hot:
RoadComfort™
They are fairly easy to install, as long as you have some mechanical aptitude, and can just think things through while staying calm lol.
But really, i love these heaters, ive been using these two types for over a year now and have never had a complaint about them. The wire filimant one will get hotter than the carbon fiber one, but they are smaller pads than the c/f element pads. I Usually use the wire element one unless my stock has ran out and i have one that cant wait till i get more so then i use the c/f element one. Another reason i would use a c/f one is if i need to trim holes in it to make it were i can reatach th cover fasteners to the seams in the cushions, becahse you cant trim the wired element ones. So i will use a c/f one that i can trim if i need it to go over a seem thats attached to the foam or something like that. But generealy 95% of the time i use the wire element pads.
Now although i havent done a kit in a mustang from what ive heard from talking to different installers in the mustang seats the covers are glued to the foam in the seams, instead of using hog rings or velcro like most everything else. So it could be tricky to get it to look perefect if you dont have much apholstry experiance. And if they are glued like ive been told there is a chance you might damage the cover or foam seperating them and then putting them back together.