The downside, as I see it, is that if they achieve wide adoption or even by those who elect to use them, there is a very real possiblity that they will effect certain player's play. Like shinguards, knee pads, etc. there will be players who will use them for more agressive contact. Rather than head contact being a painful accident, players with protective gear, may integrate it into their playing style, which, as in football and hockey, could theortically increase the number and seriousness of injuries the headgear was developed to prevent.
