I am currently using one on my 20gL tank. I was on a budget(I am a broke college student) and I got it from a friend for free so I figured why not, better than my dimmer... its an on/off style tstat and with a little fine tuning it holds my temp at 92 +/- about 1 to 2 degrees. it will get two 92 or 93 then shutoff and drop to 90 or 91. I cant complain about that!
I was using a dimmer prior to getting this zilla tstat and my temps would fluctuate way too much for my liking, so no I have my Infrared Bulb plugged into the dimmer and I can tune the hot side exactly to 90 +/- 2 to 3 degrees.