I did research this topic many years ago during the bird flu panic, and the short answer is yes, a PROPERLY USED N95 mask prevents infection. The properly used part is quite tricky though, for example you touch the outside of the mask with your fingers when you remove it, and then rub your eyes... There's a reason those guys are in a full suit and not just a mask.

But even if it's not 100% effective, even if it's just 90% it's still a massive win.