I like, too. I even bookmarked the product page. But if I recall correctly, there's a 1:3 reduction in there which makes taking it up to reasonable (heh) speeds pretty difficult, and you can't go very far when the temp rises. So, you'd pretty much need a trailer and another truck to take it anywhere.
All in all, they are terribly impractical. Which is too bad, because it would be AWESOME to see a set on a VX sometime.