My boss had a set of aftermarket heaters put in his wifes last car. when he went to turn the lease in, i asked if i took them back out if i could have them. he said sure since he was going to turn the car in as is anyways.
Took me maybe 2 hours to remove them from his wifes 300C. and then another saturday afternoon after work I installed them in my F-250. I've never had heated seats before, and I can say i love this mod. pretty easy to do.
I'm not sure what kit I have as I got it free 'o' charge just a little labor, but it looks similar to yours. it has the same high/low seat rocker switch and similar wiring although my heating elements just looked like a piece of screen mesh with the heating "wires" stitched on it.
passanger side took me about an hour, drivers side took me about 20 minutes after I knew what I was doing! :) nice writeup!
as for longevity. the ones in my truck lasted 2 years in the bosses wifes car, and have now been in my truck 3 months or so. I would say if they crapped out tomorrow they would be worth the $120 for a few years. but mine are still good and working fine!