Are you saying the masks are helpful to prevent contraction of the virus, or to stop the spreading of it from those who are contagious, but don't know about it yet?
From what I understand the best prevention is to reduce face-to-face contact with other people where possible, but an N95 mask would definitely help prevent contraction in public spaces.
Of course, these measures seem extreme since ~80% of people will barely notice they are infected / have mild symptoms, but it's all about peak-load reduction.
[1]: https://www.youtube.com/watch?v=V1xBiBVH7U4 [2]: https://www.youtube.com/watch?v=E3URhJx0NSw&t=7s
It gives you very limited protection. There's no replacement for just avoiding people, 15 feet away from everyone.
They're mainly good for people who are infected to not transmit pathogens.
When doctors operate on infectious people, they wear hazmat suits. Full face mask, air filter and body condom. You can get a virus through your ears, eyes, mouth, nose, or microabrasions on your skin.
You can wear a mask, but I fear that people will start thinking it's anywhere near full protection. False sense of security is probably not worth even encouraging in a situation this dire.