When I first started doing headlight restoration as part of my business I had one of those powerballs - biggest freakin waste of money ever, thing was unusable after about 2 sets. The metal rod that attaches to the ball is basically left unprotected at the top center. As the pad wears the flaps lay out flat, exposing a very hard center piece and making the ball nearly impossible to use w/o running serious risk of damage. The ball is not completely useless, however, because it does serve it's purpose on polished wheels with hard to reach places.

Also keep in mind with the product posted the picture on the cover of the system is not an accurate depiction of results expected with materials provided. For very light yellowing/hazing a proper pad and compound can make lights look like new but that is not a typical case.