I actually really like the idea and am really not very concerned about shark attacks. There are places where I might be but not where I would be kayaking. It's a great idea to have hands free. A pedal prop might be nice too although it's probably prone to damage. A tunnel vee prop yak... OK now I am getting a bit carried away.
The animation appears to suggest a little up and down motion while the fins operate.
I wonder if you can flap one side to turn.