i think the koolance is the best of the external systems. however, a DIY (when done even moderately well) will outperform the koolance/corsair/etc. the draw of those is the ease of use. they're more compact and stuff like that.
if you want performance over ease of use (just initially, and maintenance can be easier on DIY if you do it that way) then go DIY.
if you want something you can have running in 10 minutes (or less) then go koolance.