Pros:

-Best for military skin mods.
-Feels like you're on a mission.

Cons:

-There are 2 image that appears to be the same, while in game.
-When downed, the image is just plain horrible. A sniper unit... what the hell.  

Conclusion:

Very good for military skin mod. Very bad image when downed. 

Pros:

-Feels like a soldier
-Suitable for soldiers with mask
-Best for playing in single player/Campaign . (I will explain it in the Cons section).

Cons:

-It doesn't fit in versus mode, as I am wearing a mask while i'm in the Infected team. -0.5
-Cutscene made me fly due the gas mask lmao. -0.5

Conclusion:

It's an awesome gas mask. Good for being in a soldier unit feel. Suitable for single player, I always turn it on.