Sounds a bit like my relationship with No. 3 (who flat out said she'd never done things like email with a client the way she did with me) and maybe No. 1. In those cases, I think they were more trying to mother me, and yeah they had good intentions, but in my case those were the paving stones to hell. It might work out great, but there's a risk.

Also, growly, shouldn't he sign a waiver he won't sue you if you get into an accident while he is in the car? I don't mean necessarily for injury or things insurance covers, but if it's an issue of trust it should go both ways.