Hi, and welcome to the forum. I saw that website a while ago and thought that it was an interesting concept. There are also a few other manufactures now making outside forced hot air furnaces too. I would think that for a small home or trailer type home it would help with reducing the heating cost, but I'm concerned with actually how long of a burn time one would receive from such a unit that small or how many years you will get out of burning in a 55 gallon drum. I guess that it has it's place in the market and would think that it will do what it says.
Here is a link to another small custom outdoor furnace fabricator that may suit your needs better. http://www.youtube.com/user/futureofblueskyscom
His name is Josh and he has been making these units for a while and I understand that they are pretty well built and insulated, plus only a few more hundred dollars more. If an inexpensive outdoor hot air furnaces that is built to last longer and burn longer is what you are looking for, I'd give this guy Josh a call too.