They aren't 'random' per se. Typically you'd find one online and look at the reviews and ask people on forums about it. The aftermarket car audience is very o

They aren't 'random' per se. Typically you'd find one online and look at the reviews and ask people on forums about it. The aftermarket car audience is very online, much like HN. Getting into it, again like with programming, requires a fair bit of knowledge/mistakes. But, you gain knowledge and get better over time. If the electronics screwup your OBC, you can just get a new one. If they screwup your wiring or blow your engine, well, you don't get into cars if you don't want oil all over your arms. Blowing things up and rebuilding engines is part of the 'fun'.