I've been using the fins since AL Warnike first came up with the concept. He passed me some prototype fins, and I've been testing them and giving him feedback.
Basically, they work as long as you have a LOT of forward speed (speeds well in excess that the Robson kayak can achieve). At slower speeds they create more drag than anything - at least that was my experience. But once you're flying - like in a surf boat, they are a nice mix between fins and no fins... so things like Helix's etc are still super easy, but it gives the boat some bite in the wave.
After about 6 months using the fins, I've gone back to traditional foiled fins... not that the concept isn;t wrong... maybe it just needs mre development.
Hats off to Al for making the fins!!!
Corran