I saw these at Canyonlands 4 and have never seen any like them.
I've never seen another set either and when I found those I just had to have them. I know Warren Rollins has seen them before because they came from him a couple years back at chickasha swap meet. They are on the same axle I got from him as well and boy was it bent.
Must admit, I did think that I had seen them before. They look good and should smooth out a very rocky road.