I'll be honest: I would never use one of those machines for a few reasons: first of all usually they have very high commission compared to an exchange, and that for me would be more than enough to avoid them. Secondly, I would add also a security problem: someone could wait outside and follow you home with the intent to rob your wallet. Maybe that was the first time you ever bought bitcoin, maybe you have a ton of them at home, who knows, that person for sure doesn't know and could have his own ideas about what you own...