During the time I had mine I never needed it. However I dropped my piece at a friend's house and it fired. It blew up a table and bounced up through the roof. My friend and his father who owned the house were not happy about that incident. It also scared the piss out of their dog and it has been on Prozac ever since.
But seriously, consider your reasons for wanting to carry a weapon. If you hang out at places where trouble is likely to occur, find another place to hang out. You don't ever want to be in a situation where you use that weapon because even if you do defend yourself you will still likely have legal problems.
I had mine while I was a pizza delivery driver. Unfortunately, pizza drivers are frequent targets for thugs. I'm still not sure it would have ever helped as the thugs always have the upper hand since they are making the first move.