They're dangerous to use even when functioning properly without a controller. They can reach 100+ degree temperatures in a hurry, which is definitely too warm for a BP.
Check out this awesome discussion/guide if you want to stick with the fish aquarium route: http://ball-pythons.net/forums/showt...With-Pictures!
Also, I'll also put in a good word for the Herpstat thermostats. I have three (a 1, a 2, and a 4), and they're all awesome.