The Bathmate has a self-limiting mechanism. Those bellows will only create a certain amount of vacuum. It is probably enough vacuum to injure yourself with, but only when you are unconditioned, or if you go for longer than the maximum of twenty minutes. I have read stories on here of guys who have injured themselves with their Bathmate. When I started with mine I would only use it for ten minutes at a time. I quickly, like in a few weeks time, built up to using it for twenty minutes at a time, four to five times a week. I feel like you would have to be almost trying to hurt yourself with a Bathmate in order to get an injury.
Seems that isn’t true from somethings I have read on here. I don’t know what is best, but it is likely whichever is cheapest. I have an air pump, and a couple of Bathmates, and there are pros and cons to each system. The air pump was a good deal cheaper though.