I've heard hundreds of accounts (not literally, but close) of people getting hurt in weight vests.
When you think about what a weight vest does, any additional gains you'd be getting from it are pretty insignificant.
That said, if you're into the whole high risk/low reward type of stuff, buy one and keep it as light as possible for 3 weeks or so before adding a couple pounds, then another 3 weeks, then a couple pounds, so on so forth.
Good luck with whatever you do.