its a difficult one, but all paint will break on them including hard as hell site paint. i will agree it will add a bounce factor, how much by is i am not certain. In my opinion its not as high as some think.
Just becuase you are wearing one doesnt mean it will bounce, though it probably will help. I do wear one when ever i play, ref, or marshal at a site and why, i get shot at normally 4+ days a week upto 7.
To be honest when you get bruise after bruise in the same place they do start to hurt more. And yes i know the pain isnt that high but they can hurt, i even know my bro popped cartlidge in his ribs when shot without one one. Would it if stopped it who knows. Could it of helped to reduce the chance, Probably Yes.
I dont care if i get called a girl but im going to carry on wearing one till they are outlawed. For 2 reasons, to reduce pain and give me a slight advantage when i play.