Those are really useful boxes they do have the best lids I have ever seen I don't know if I would trust the 100% however. I agree with Jerry flexwatt cheaper and easier if you have a bunch of tubs but one, no the added safety of ultratherm or intellitemp have it all over flexwatt and with a single animal it isn't easier to wire flexwatt at all.

I don't like on off units full stop, they are ok if you have stable room temps, with indirect heat or really heavy enclosures. I don't feel the nature is wise with thin material in unstable room temps that are common among fist snake owners whom choose tubs. Tanks they are fine, plastic enclosures and racks but single tubs are to thin and too directly attached to buffer the cycles of temp. Especially with the units designed to heat dirt where the probe is heavy and slow to respond.