This does look really cool, and they appear to be doing it right (IMAP + OAuth), but I'd feel really weird about giving a third party access to my Gmail account

This does look really cool, and they appear to be doing it right (IMAP + OAuth), but I'd feel really weird about giving a third party access to my Gmail account and letting them futz around with messages. I'm sure they're very careful and all, but if there were ever a data loss bug -- especially one that wasn't immediately obvious -- I would be very, very unhappy.