A few disadvantages, the biggest is that BBs can fragment and make their way through the mesh. Happened on my very first airsoft game with the rental mesh masks had a fragment come in and tap me just below the eye.
In addition the vertical pattern breaks up your vision in such a way that makes tracking BBs much harder. It darkens the vision but the tracking is more problematic IMO.
They only survive a small number of strikes in the same place so you should replace them after a number of strikes.