Claims 465mph on 500hp? It took nearly 2,000hp to get a sleek S/E fighter to 400mph and I don't suppose the physics have changed, even with laminar flow and it has probably twice the cross section.
On a 500hp diesel cruise is probably only 400hp at best and even with the torque a diesel puts out it still has to do the work for the whole trip.
Pusher props are inherently less efficient than tractor (I know, I had one!) As the drawbacks stack up you have to wonder how the figures will work out in practice.
(On the other hand I would really have liked to see the Aluminium VW V10 engine in an aircraft!)