A surgical mask is intended to be worn by health professionals during surgery and at other times to catch the bacteria shed in liquid droplets and aerosols from the wearer's mouth and nose.... Link
IMHO, a mask is better than nothing; but it is far from what I would term "effective protection". I'm not a medical professional - just a silly engineer. Still, any filter is better than nothing, but a filter that is 100x larger than the viri is practically useless, IMHO.
Sure, the virus is small, but it is carried in droplets, which are much larger.
I don't think viri propel themselves across space. I think they need to be transported by liquid droplets, etc. Yet, I am not even a silly engineer so what do I know? :-)