Is there a particular reason you would want one without the other? Just curious as I turn the seat off as soon as the heater is working properly.
I think some people want the back of the seat heated, bu don't like the hot butt. There were a few people a year ago in Southern California that were trying to disconnect the seat bottom.
At that time I didn't understand how the factory wiring worked. I looked into wiring my car with factory heated seats, but it's too much work. The controls are in the dash, there's no wiring avalible, everything would have to be run. I also needed a heated seat module from the bottom of the drivers seat.
Aftermarket directly powered was the easiest and cleanest. If I leave them on too long and burn my skin, I have no one to blame but myself!
I couldn't believe the safety guards that the OEM seats have!