Ian,
I do have a Windpaddle. They are almost magical if you take one along with you you will always experience a head wind. If you change directions the wind will also change directions. They work great when the wind is right. Some paddlers find it really confusing to fold them up again so it is worth buying two just to watch your paddling friends fight with it when it is time to put it away. It is pretty simple once you figure it out but it is a 2 hand process. My only complaint is when I put it right in front of my cockpit if I want to still use my paddle I need to either tie it to my PFD or loop it around my back and I don't like being tied to anything. If I were to use it a lot I would rig a way to attach it a few feet in front of the cockpit and still be able to retrieve it to fold it up. That way I could attach the tether to the paddle park. I have met the guy that owns the business, he seems like a good straight up sort of a person.
Scott