I run a manual "pull to release" system in the race car. I just would hate the thought of an automatic system discharging at a very inopportune time.
I'm not sure how I feel about having a full system in a street car, but I would (and do) carry a bottle in the car with me at all times.
I'm never worried about saving the car (in case of fire) just buying enought time to get my butt out of it!