I don't see how they can claim a given speed.
So much depends.
With a turbine you do get a more efficient cowling shape, generally. But the fuel is heavier so you get less range even for the same SFC, and no turbine will match the SFC of a correctly leaned piston engine.
It's lighter but that merely severely screws up your W&B, requiring a very long mounting frame - see the
Jetprop conversion. The resulting position of the nose gear could impact (pun intended) the prop clearance on grass
I'd like to see the real fuel flow at say 240HP, ISA. If they are doing 18USG/hr then they have a sterling proposition but I think they will have bent some rules of physics doing that because
AFAIK nobody has got anywhere near that before.