Hi Antony ,
that ´s a good question and many many people have asked me that in the last 5 years.
The big difference between a jet and a propeller drive unit is the way the board turns in the water.
My main intention was since the beginning in 2010 to get a “real surf feeling” also in flat waters.
With a jet you can go much faster but with a propeller drive unit you can make narrower turns without a rope or foot straps e.g. and you feel completely free on the board. The feeling is completely different.
And one important thing is a prop-drive is much more efficient than a jet drive. That means you will need less battery power that means less weight or more runtime.
Other big advantage is you can surf in small waves or even in choppy water without a big stall which happens by jet drive systems and a prop drive is much quieter.
One little disadvantage is the rotating prop, that´s right. Because of this we have constructed a protection ring and wings to minimize the injury risk. This ring takes a little bit of the performance of the board but it´s still sufficient enough.
If you fall from a jet-boards this board move on very fast 15-25m until they stop. (The waterwolf MPX-3 stops in between 2-5meters) In combination with their big sharp fins they are more or even equal dangerous for swimmers then a prop-drive board. The waterwolf has no fins because the motor unit stabilize the board perfect.)
by the way: MPX stands for Motorized Propeller Dive unit
Summarized I can say:
Both categories of board have strengths and shoals.
For racing the jetboards are better suitable and for surfing waterwolf is more suitable!