While logic seemingly would indicate that the hockey masks are safer, they have not proven to be so at the ML level.
Every ML umpire wearing a hockey style mask last year suffered a concussion. Granted the time frame is too short and the sampling too small for this to be scientifically significant.
No doubt the same blows would have resulted in a concussion with a traditional mask as well. However the failure of the "shock system" on the hockey style mask to perform better than a traditional mask is, to me, interesting.
Here's a particularly violent example.
Kerwin Danley