I have had better luck with jumpstarts than the exo 300w, both are on/off except had way more fluctuation with the exo terra. The 600w exo is proportional, and kind of seems like a cheap version of the Herpstat what with night/day mode and all, but I can't imagine it comes anywhere close to the quality, reliability, and safety of the herpstat. Also, though it is expensive, the herpstat 4 has 4 probes/inputs and has so many other cool functions so if you can afford the investment now I would say go herpstat.