It makes me wonder about control issues: I would think that this one doesn't have enough degrees of freedom to both turn and propel itself. But then, I could say the same thing about a one-string kite: really all you can do is pull or let go the string, giving you only one degree of freedom to control it, but still kites can be flown and controlled. And obviously, this one can be flown as well.

(Via MF)