If you take the balls out and lock the diff it will loosen unless its pinned. The biggest advantage to a spool diff would be weight loss. With 2.5 million in my gear diff it's for all practical purposes locked but its heavy. 25.5 motors lack balls they make good rpm but power is minimal so lightening the axle assembly plus the ability to hook up immediately could prove very beneficial. I just would like to try it if it's easy to use existing parts or I will just make my own to try but would prefer the later.