Herpstats are great! I have a Herpstate II and love it. Proportionals are better than on/off's in my opinion, they regulate the heat more even than apposed to letting the temp. drop down to a certain temp. then turning on and raising it back up then shutting off again. Proportionals just lower the power to the heating device when it reaches the set temp. then increases it to raise it back up. Never shutting off. Helix is a proportional as well and a very good thermostat. Now some of the Vivarium Electronics are Pulse Proportional OR On/Off capable, the VE-200, VE-300 and VE-300x2 are, the VE-100 is not, just on/off.