Oh boy, this should be a good one, I have run several gassers, WoodDoctor, Sequoyah Paradise, Empire, Portage and Main and very soon will be running 2 HeatMasters so as you can tell I have been around them a bit, I started with a WoodDoctor, Energy Converter they called it, what a great improvement over the conventional wood pigs, very clean visibly, enough to run without issue at several shows, at the time we were the only folks burning a wood boiler at any shows here in the northeast, they had some issues early on with solenoids sticking and burning out but then went to a Honeywell servo motor to open the draft and that issue disappeared, firebricks used as nozzles needed to be replaced every couple of years but this was an easy task, the biggest issue I saw with the line was that the manufacturers did not pay attention to the rotting out issue, there is lots of speculation about why they rotted out, I happen to think it was profit driven and they cheaped out on steel quality, had they addressed that issue early on they would more than likely still be around today with a top of the line unit!
Sequoyah Paradise, for the first run of gassers, this was a great unit, huge firebox, not as clean, only phase 1 so we were shut off here in Maine very quickly from being able to buy or sell them but aside from electronics issues with the solenoid and that darn love controller they were pretty reliable and would burn what you threw in, I sincerely wish they had retested for the phase 2 standards.
I do not want to make this long winded so I will reserve my comments on the others until some other folks have chimed in, my suggestion to all the manufacturers is to pay special attention to making your units last in the field, never mind the EPA test it can be overcome, build a simple, reliable, long lasting unit!