Wow, I feel sorry for the manufactures that build wood boilers with out grates. How does the wood burn? Lol The only wood that didn't burn in my NCB-250 was water logged.
All conventional (updraft) wood boilers work on the same premis, add wood, fire, air and try to extract as much heat as possible before the gasses excape out the chimney. Nature's Comfort has invested a lot of time and money in the developement of the NCB series wood boilers. They used computer modeling to show the flow of the water through the water jacket and used diverters to force the water in the hot areas to extract as much heat as possible. Even the chimney water jacket was computer modeled to promote water heat extraction.
I have been a territory manager for Nature's Comfort since 2008 and I can tell you that the latest generation of NCB boilers are a very well designed boiler. Not only did Nature's Comfort try to make a wood boiler with all the engineered benifits but they also listened to the customer feed back and implimented common sense features. The boilers are lazer cut, and robot welded. The craftsmenship of the parts are consistant enough to exchage from one unit to another without any misalignment. The electronics are simple in design yet versatile enough to allow a generator back up.
With all that said, I also know the some of the other manufactures also build a good quality wood boiler. It all comes down to the customer preference and the biggest bang for the money. Its no different than Chevy vs Ford or Dogde!