I have one of these :
Mask
To test how strong it was, I emptied a 30 round mag from an M4 into it, from 15 feet away. The paint on the visor is chipped, but its still intact. BBs also mark the the mask where they hit the plastic, as they leave white scuff marks.
I went for the mask because my parents at the time wanted to make sure I kept all my teeth (something I'd like to do). Until I can find something that gaurds my teeth/mouth, but isn't a full mask, I'm keeping it.
The cons - well, because this is mesh, it doesn't fog up. My glasses under the mask though...
View is definitly restricted. Take a look through a letter box. Your vision is limited to the space of about 2 letter boxes, one on top of the other.
ADS - you may find it difficult to aim down (IRON) sights with a mask, as it bulks your face width up. I've found it near impossible to ADS with an L85 - however, when a scope/sight unit is added, its easier (you can angle your head and the eye-bit is bigger than iron sights)