I think the legal aspect of the issue has been discussed.
Regarding the safety aspect, a friend of mine fired one out of his CZ .22 rifle. The round didn't even make it halfway down the barrel. Lucky for him, neither of us saw an impact, so we checked the barrel. Sure enough, stuck in the tube.
I would not trust these in a rifle at all, and will avoid them in general.
They were quiet though...no sub for a can of course...