I did a lot of research on sniping services before going with Gixen, and I feel that I made the right choice. Every auction I've used it for has worked perfectly. The interface is simple and user-friendly, and it has all the features I need, plus some I haven't had an opportunity to try yet. The Greasemonkey add-on created by one of the Gixen users is a great touch that saves some copying and pasting.
Security was the feature I was most interested in. I'm an experienced network administrator, and wouldn't trust any product with my login info without being 100% confident that my credentials are secure. I'm sure that my authentication information will not be compromised by Gixen. Passwords are automatically deleted from the Gixen database 48 hours after a bid is completed, which I haven't seen offered elsewhere. I saw some of the reviews claiming that passwords had been compromised while using Gixen, but further research shows that these people were more likely victims of phishing or other similar scams. I highly recommend this service. It is invaluable for any savvy sniper.