I was in attendance at the Chicago Comic Con. I stopped by the CGC booth and tried to talk to one of the staffers on site. I asked a young lady (Once I got her attention) "if their cases were better than Mylar?" She replied that they were "because they were bigger and offer more protection."
While I'm not detective or anything, I quickly deduced that Ms Obvious was not the right person to sell me on their seeming polypropylene product vs mylar.
I am still left unsatisfied on this point. Overall my opinion has not changed.