Acutally I have used it. It's been sitting around on the shelf since about a week after I got it, way back in the early days of getting my first snake. It's a waste of money, but it does seem to work.

It's late, so I may not be thinking correctly, but if the ambient temperature continues to rise, the rhoestat will maintin the heating element (pad, lights, etc.) at the appriopriate range, but with the ambient air it may still get too hot for your reptile. Thermostats are much safer, although a more expensive.