Has anyone on this site got or used a NSD powerball?

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Hey all, i have a NSD powerball, and i was just wondering how badly i am in the minority? I only know of one other person who has one, and i was wondering how good it actually is at toning up your forarms and your grip? I have began noticing a differnce, but i cant help but feel it may take a long time compared to handgrips? There is also another product i have heard about called xtensor. I was wondering if anyone has this either? Thanks