Actually, it was a diesel mechanic who put me on to it, for starting a very old diesel pump motor. And he's a very good diesel mechanic. As for me personally, I've found it very useful for getting two-stoke engines that have been left sitting for >3 months started. One quick spray, and they start first go, and then keep running fine (and restarting without the aid of it again). Enlighten me as to why "absolutely no professional would use crap like that"? And as to how you know this about all professionals?