I was under these weren't really a chiller but more of a heat exchanger.
I recently found two of those on ebay that were used by someone with a 55 gallon tank. They were selling 2 that weren't getting the job done in favor of a larger chiller unit.
Reef raf has a smokin deal on a used chiller right now. Worth every penny for peace of mind and a nice cool reef IMO.
http://www.canreef.com/vbulletin/showthread.php?t=29962