My impression of mask effectiveness for aerosolized illnesses like COVID (it doesn't spread primarily through spittle, unlike what a lot of public health authorities assumed early on in the pandemic when the initial mask recommendations were made), after reading the arguments on both sides during the pandemic, is that they can be usefully analogized to birth control methods:
- Surgical masks: douching after sex. Probably has some small effectiveness compared to doing nothing, but shouldn't be considered as a serious method to prevent propagation.
- N95-level masks to prevent transmission: coitus interruptus. Definitely effective, but also almost impossible to use at anything resembling 100% effectiveness. With coitus interruptus, pre-ejaculate and general inability to precisely control ejaculation mean the method will assuredly fail after a while. Analogously, N95 masks would probably significantly reduce transmission if everyone used them, although probably not to 0. But outside of hospitals, compliance is probably not strong enough to significantly affect the progress of an infection wave.
- N95-level masks to protect against infection (including masks with vents): condoms. Almost 100% effective if used perfectly, but can easily still mess it up on occasion. N95 effectiveness is much worse than condoms in practice outside of hospitals because masks have to be worn for the majority of the day, unlike condoms, which are only worn during the sex act itself.
- Abstinence: staying away from any carriers. Unlike with sex, almost impossible to do for a contagious respiratory cold-like pandemic like COVID.