You mean between those commercial units and the HM? I've never owned any of them but I have heard people talk about selling off those units after building a Heater Meter. The HM has flexibility and features you're not gonna find in other units, like for one most of the commercial units don't ramp the blower speed, they just pulse the blower on and off at one speed. The fan on the HM is completely variable so you don't get the puff puff puff like you will from some of those other units, unless you set the HM to behave that way which you can do because it is so damn flexible. Another option that I don't think any other commercial unit has to date is servo controlled damper, which can actively regulate convection air flow by opening and closing a valve. It's like a hyper vigilant pit master constantly adjusting your vent while you go on about your business enjoying life! There are too many features for me to name, the only feature I know of that the HM doesn't have yet is PID auto tune. I know Bryan has taken a stab at that more than once but said he hasn't come up with something that works reliably. Some commercial units say they have auto tune but I am not sure how well it works. TBHWY in most situations I think the stock PID values work pretty well with the HM though....
