That is a very interesting design! But, for 3900 Euros one could buy almost (2) R65s, or a very pristine airhead of any displacement..

While it looks great for smooth surfaces, I don't know how stable & comfortable it would be on loose/gravel roads where I live, or on city streets of Boston or New York where the typical pot hole is half the depth of the larger wheel on that device. Nonetheless I think it is a very clever design.