Ash, I was looking at those too.
Depending on the size of your cabin, and building codes (if there are any in that area), they seem very efficient. But if you look into them more, most people using them are in fairly small homes and most of them are earth made houses. You know the hippie type in the north west. Another thing is the exhaust, most building codes require the chimney to be above the highest point of the building, if you make the heat exchanger to long it won't have enough force/draft to go that high.
Now to use the same principles you could make something similar, look up a masonry heater or Russian stove, it's almost the same thing but made of brick or stone and looks like a fireplace, the exhaust gases pass through several turns before going out the chimney or pipe. You burn them hot to heat up the masonry and that slowly radiates the heat.
Actually a steel/cast iron stove (wood or coal) can be turned into a mass heater, build up brick or stone around it to hold in the heat. And if you put a thermometer on the stove pipe before it goes into the chimney or exits the building and your getting readings over 300 degrees, you can reroute that sideways through a heat mass then turn it back toward the exit to soak up more heat.
I found info where a guy built a mass heater using a 30gal & 55gal drum, placed them inside each other so the 30 is the fire box, then he put masonry sand (crushed granite) between the two (this was the heat mass). He claims with a short hot fire it radiates heat for at least 6 hours.
I'm actually looking into doing something like this right now, the place I live in now is all electric heat and three months of the year the bill at least doubles and the rates keep going up, hopefully this will help a little and I can get wood fairly cheap or free.