I have never had Gixen fail on me. It's easy as cake to use and won't let you down. Their security practices are excellent, there's no risk to your account. The free service is incredibly reliable, but the service is so wonderful you should definitely subscribe to the service if you can afford it. They deserve it.
I don't think I need to say much more, but reviews need to be 500 characters, so here's a tip for new users: If there are several auctions for an item you're interested in but you only want to buy one, Gixen has a useful feature called groups that will cancel the rest of the bids after you win one of the auctions, saving even more of your time.