I have one.. Its not fantastic, but it will hold a reasonably steady temp. I saw one for sale at my local hydro store and thought I would pick it up just to see how it works. It maintains the temp within a few degrees, but much like a dimmer it fluctuates with the overall room temperature. It is not as accurate as a herpstat. Not even close.

Its worth the $25 if that is what your asking. If you have the money for a better stat, get a herpstat. You get what you pay for in this instance.