Had one on a hagon maico I built in 1974. Keith Stacker bought a frame kit for me through Bert Flood and it was a standard item for that years model. As stated worked on a solid rear sprocket and it was more effective to drag a toe in the dirt than use the mechanical disc, but it did get you past scutineering. Value would be in its uniqueness, but anyone into racing would ditch it for something better.