It has or more properly HAD more than a few problems.
The design with the Pilot Above the wing made stability very marginal.
The speed window between where it lifted off and where it became unstable was well less than 5 mph.
If the boat driver way not extremely accurate on the throttle and the observer didn't call out the speed adjustments. It ended badly.
The person on the tube needed to understand aerodynamic stability, Weight and Balance, or it ended badly.
Add any alcohol to the mix and it ended badly. Typically like
This.
Having said all that, I think there is a market for a well designed flyable towable.
A single seat cockpit towable with a modified Kite Surfing Canopy above it, sounds like something more reasonable.
A couple of toggle lines to the canopy for the rider would allow control of the flight, Left, Right, Up and Down.
For example, if the rider did not pull the control lines, it would not take off, and it he let go in flight, it would land.