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.

There's very little evidence N95 masks work better than surgical masks, which are cheaper and easier to use.

Umm, properly used N95 masks have been shown to filter particles <10 nm...

N95 masks are better when there's dust, or smog, but don't make preventing getting sick any better than surgical masks. The idea behind surgical masks is to prevent you from getting sick when people sneeze, cough, etc. So the effectiveness is basically the same providing you use them properly.

Never touch the front of the mask. Wash your hands after removing. Dispose of mask after use.

And repeated studies have failed to show that N95 masks reduce transmission more than surgical masks do.

One of many studies: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4868605/