If it is in the mid 30's outside, the seats in my E39 feel cold for at least half an hour. The cabin will be toasty but the seat still sucks that heat out of me.
It was the only option I would want that wasn't checked by the PO when he ordered it so I added it. No regrets!
These ebay/amazon "carbon fiber" elements do not hold a candle to factory BMW/VW seat heaters. They take about 5 minutes before you really start to notice they are even on, but after 15-20 minutes you have to turn them down. They draw about 2 amps each.
We did some digging and the Dorman elements draw 3.9 amps per seat making them the most powerful aftermarket ones I have found. No one else publishes current draw, I only have that data from installing half a dozen sets myself.
