What's wrong with this engine?

While I cannot speak with absolute authority, a volkswagenesque engine
that needs to run at 7300 rpm would not seem like a high hour engine...

AL

Holy crap! How does Limbach do that?

Now, since it develops max power at 7300 rpm you'd need
a 2:1 speed reduction or so to use a 48" prop, effectively,
right? Supposing the speed reducer DOUBLES the weight, it's
still pretty darned impressive. According to what I can find
on the history of Limbach, the design is based on a VW, but
is built from the ground up to be an airplane engine.

So, what is the down side to these engines? Do they cost a
gazillion dollars or blow up at 20 hours or something? There
has to be a downside somewhere.