They never seem to catch on for some reason. They popped up in the late 1800's and seems like every 20 years theres a new design, but they don't stick around. I like the idea, though it seems like it could have some small issues. The main thing I don't like is the fact that the fuel travels to the engine through the hollow axle and through some type of banjo bolt. I think that the high wear on that location could cause it to leak fuel should the connection get worn. The engine doesn't idle when you come to a stop, kind of an interesting design. Its possible it was used to decrease emissions. The price does seem to be below other wheel motors such as the sachs saxonette.