Oh, the poly patch. As effective as the foaming bore cleaners and barrel seasoning lube :rotf: . These gimmicks are out there for only one reason, and that's to take the money in your pocket, and put it in the seller's pocket.
Aside from the danger Zonie mentioned (which is a biggie), the plastic cups were too slick to effectively transfer the spin to the ball. For the most part, the cup would just spin around the ball. I also heard that they would leave melted plastic in the rifling, but that may have just been biased propoganda.
There's a reason we use a lubed patch, you just can't improve on that system, only tweek it to make it better. Bill