i have one of those powerballs, mine is actually a 'powerball' brand not the dynaflex, i researched the differences, and the differences is that my powerball can just spin alot faster. Roughly up to 15,000 rpms, good luck trying to get up there!!! my fastest was 11,000 and boy is a extra 1,000 rpm hard.... but i use the thing to warm up and get my arms loose i find it VERY good for warming up when i'm in the car (not driving) and once i'm on the court i'm all ready!