The explanation video is so full of bovine excrements it is actually quite funny.
Any lift from the winglets will provide drag. The design of the starfin is made for crafts rolling to the side (sailboats, then surfboards) so that a winglet becomes vertical and compensates the tendency of the single fin (or sailboat keel) to "slip" with roll angle.
Note I had a Starfin on my 6'6" SUP nearly 5 years ago... (pic below)
The issue with it is that, depending on the tail rocker, the winglets would induce extreme drag if not properly aligned with the water flow. But with the proper angle, it is quite fun, you get a single fin that keep its bite in turns. Alas the vertical, "spitfire" shape is quite twitchy in turns...