If you are wondering the cost difference there are several issues to address. running a proportional thermostat means it is sucking power all the time. It is a steady amp draw. The Johnson controls turn on and off. You would have to know how frequently they cycle on and off and time from on to off. Some say it is more efficient to run the on off. I found that I saved about 20 bucks a month running my herpstat. So i say it is cheaper to run proportional. It also does not spike your heat tape. An on off spikes giving full power till the temp is satisfied. I think its a personnal choice but thats just me.