I used a similar device on my Pico 5gal tank with a 150W MH light.
Although my temp gague did not turn on and off fans, it did lead me to a issue you did not mention yet.
the power for the "unit" needs to have both 5 and 12 rails, not just the single rail set like the power supply you listed.
My work around was to get a cheap "PC pewer supply " from wierd stuff wherhouse, that in used for the power of the fans, and the temp unit itself.
build thread:
http://www.reefcentral.com/forums/showthread.php?s=&threadid=1509864
pics:
Was built for Pico challenge, for a club event, but the club imploded, and so did the contest.