paolo,
on auto cars I'm not biased - I WATCHED a MANUAL VEHICLE start and PIN a 5 y/o girl TO A WALL - I have a REASON for stating what I do. I was not responsible for the work on that car but I knew FULL well how it happened. it had a makeshift neutral safety switch that failed - car was IN GEAR and it started.
they are good for warming up or cooling cars off on seasonal times but not much else. I see it as a 'look at me ' thing.