Unless there is a patent in place or at least applied for this is clearly a case of Capitalism. Not sure what needs to be done as far as changes to make it "Your own" design. When someone sells item for profit is when it becomes a legal issue in my opinion. If you have rights Paul I would use them, maybe a friendly letter from your attorney would help the situation. Surely Kurt should have known better but may have been a paid endorsement like so many are now.
Unless there is a pending or issued patent, anyone else is free to copy the design with impunity. While the moral question of copying someone's non-patented invention blow-by-blow is open to debate, the legality of it isn't. I see no violation of patent law here.
And if the original inventor has been selling, offering for sale, or has disclosed the invention to others for a year or more, his right to file for patent protection in the U.S. has expired.