Hi,
Here's a link:
There are several brief videos on the site, and the narrator says they get "nearly 60mpg". They are fast: up to 250kph, so with a smaller more efficient engine, then could do very well. Years ago, I read about then in Cycle World, and they were quite expensive: $100K sticks in my memory, but I could be wrong.
[Edit: the site says $79,500.]