Super singles have been around for about 50 years, at least. A fellow named Dick Cepek was selling them for folks using their trucks in the Baja in the mid 60's. I bought a set to install on the back of my Ford Camper Special pickup when the original 16 inch tires wore out. Gave more load capacity to carry the camper on the back. Never noticed any better fuel mileage. I thought they, being tubeless, were more reliable than the old tube type 750/16's. Never had a flat, but only a sample of one. As others have posted, best for flotation on soft ground, but of course I was replacing a single with a Super Single.
Biggest concern I would having using them is when you blow one on a long, lonely road in the West, where will you find a replacement?