The Security Six is the forerunner of the present GP series of Rugers. It's one of those guns that is arguably better than its sucessor: light enough, brutishly strong for a 'medium frame'; and more than adequately accurate, if you can accustom yourself to the 'non-S&W' trigger action, Many people criticise this last item, but I see it as like complaining that watermelons have seeds and pineapples don't. You can get used to either one, and inevitably hate the other.
If you can get a blued one for under $200, it's worth buying; stainless and near perfect would go for around $300 and still be a good buy.