I saw one of these in Hawaii this year. We were snorkeling on the Big Island and a buddy of one of the crew came up to the boat and tied up to the back. He let a few people go for as spin. It's not incredibly fast, but it clips along pretty good.
I'm sure the person that invented it was a kayaker because I swear it made from the identical material as a sit-in kayak - kind of a hard plastic shell.
They would be pretty handy for getting into the hard-to-reach areas, but the price is pretty steep for what amounts to a cool toy, imho.