The section that deals with their rudder is interesting for what it leaves out as much as the purported potential of what the rudder design can do.

First:
Any rudder will create drag. If it happens to create lift as a coponent of its foil design then there is also a benefit to the boat that may or may not cancel-out the induced surface drag component of the foil.

Second:
The slot from which the rudder emerges is creating considerable induced drag at all times. It doesn't amtter if the rudder is retracted or not. The slot is still there. It is not fair, as an untouched hull surface would be and it is presented to the flow under, virtually, all conditions.

It's true that non-surface piercing foils are more efficient hydrodynamically. The claims however, generally apply to those steering foils that are constantly immersed and do not have a slot into which they can be folded, such as those found on sailboats. This one creates as much trouble as it solves.

Chris