The kiteboard in the video is quite an old design, the latest ones are much wider with much bigger fins (3x40cm).
When the wind is up they are very tricky to sail downwind though, basically the fins want to push the board out of the water.
Another advantage of the kite is that you can generate extra power by steering and looping it.
Actually hope to try one this summer, should be good fun (and also lots of swimming!).