I talked to the manufacturer last year. They try very hard to sell you on it once you contact them. I did not buy, went with rooftop solar instead.

I just couldn't find enough info or opinions on the web to make me feel comfortable that it would work. Another reason I didn't was a discussion I saw somewhere about it that talked about the basically finite amount of heat that is actually trapped in your attic compared to the amount of heat available to solar panels. My final reason was that I really wasn't comfortable having a 2" pipe pushing 30 gpm or so into my attic, possibly breaking!