I used this service a long time ago. Through it on the forums, various kinds of "freebies" are often distributed, intended for distribution on one hand.
But for private messages, I would also be more careful. Passing important information to the service is a dubious matter. This reminds me of VPN services that swear they don't keep their clients' logs. Which is ultimately sheer nonsense. If such services exist, they are unlikely to have only good intentions.