As long as they are used with common sense I couldn't see them doing much damage. The stroke would be pretty short like around an inch. Sure if you went to fast to quick I'm sure it would lead so some discomfort but an ER visit? I don't see it.
I would love one of these, but they are very expensive. The closest I have is a thrusting dildo, but it isnt that strong. As soon as it comes up against a bit of resistance it just cuts out. I need something that is going to be a bit rougher. Lol