They were popular back in the day, especially the 11x7.75. Out of a box of 6 you might get three or four that could be balanced to be usable. Quality was all over the map. They were very inefficient, but were about the best that could be had at the time. Other than nostalgia, there is no reason to run them, as APCs are far more efficient with superior quality control. Don't even think about running a Rev Up without balancing it first.