I've been driving a Honda Civic hybrid for almost 10 years now, and it has been a great car. The only thing wrong with it is the horrible hybrid battery. 120 Ni-Mh D-cells in series, no balancing system, 100 A charge and discharge currents on what are essentially flashlight D-cells! Who would have ever thought there could be a problem with that?
I also drove a HCH for 8 years. Loved the little car and would have driven it longer, but I live in south Texas where the high ambient heat caused the battery pack to fail, with fewer than 1,000 miles before the warranty would have expired. Lucky me! But Honda did not want to provide any sort of warranty on the replacement pack, so I traded the car a few months later.
Speaking of auto start/stop: At least where I live, when arriving at a red-light intersection with heavy traffic (which in theory is a situation where one would get the most benefit from such a system), the long line of vehicles would slowly inch forward to remove the slack in the vehicle queue. Therefore, less than half a minute after I had arrived at the queue, I would have truck-length gap between me and the front vehicle. The vehicles behind would honk hysterically or some would overtake me. So I had to restart the engine.
Same scenario on the freeway, with rush hour stop-and-go traffic.
So,
at least for me, this feature was pretty useless and consider it only a gimmick. The fuel savings were negligible.