As far as small machinery, waste of money. On every lawn mower, weed whip, chainsaw etc that ive worked on; Engines are tough, everything else is garbage. The deck, transmission, sheetmetal frame, seats, basically everything else will be shot long before your motor wears out on your riding mower. The clutches, head, recoil assembly are trashed before the engine on weedwacker, same goes for chainsaw. This is all assuming proper maitenance.
Not bashing, just what ive seen over the years.
As far as car engine, idk. Im skeptical.
Archoil is another one, popular with the ford powerstroke guys