I have an A star bionic bp and I wear it.
However I will have to agree that I don't believe that it will really do much protecting unless I hit something sharp (edge of a curb, rock, etc) or the bike lands on me with a peg or clip-on. Any sort of over extension, twisting or compression injury will not be prevented. I know they say they can help with an over extension but I doubt it. In fact I doubt the plastic and elastic thing will help with much of anything. But I do wear it and will hopefully never have to fully test it.