I have flown mostly plastic spinners, and have never had a problem with them in the past, they come off just like most other things when not quite installed right. I did receive a plane the other day with a prop nut on it, and i love it. from now on i will buy nothing else. now this doesn't mean i'm going to take the plastic spinners off my other planes, but as they break or crash i will probably replace them with the prop nuts.

just my humble opinion