> The ones you link to look significantly more difficult to build. This one is two boxes and a piece of plastic (from what I understand). Seems to be the case,

> The ones you link to look significantly more difficult to build. This one is two boxes and a piece of plastic (from what I understand). Seems to be the case, and looks like a significant difference. There's also a plexiglass cover, which likely helps insulate the heat inside. Simple yet ingenious, like the hipporoller ( http://www.hipporoller.org/ http://www.hipporoller.org/ ). Absolutely fantastic. For a more high-end design you can attach a heat sensor and make it electric-hybrid. Or gas-hybrid... or crankshaft-hybrid!!