Absolute essential add-on to reduce tedious moderator work and cleanup. Extensive set of options let you tweak rejection logic to suit your site making this add-on a no-brainer. Have been using for a few weeks now and can't imagine going without it for future projects.
Xon's take on this addon has been a blessing for our site. It helps track Alts, stop VPN abuse and so, so much more. We had a problematic user who after a long tale involving months and 80+ alternate accounts and several VPNs, finally got put in their place and prevented from returning to the site with this addon. Every attempt for this malicious individual to return has been stopped in its tracks since then. I won't also forget the rest of the more normal ban evaders and the such.