It has long been shown they have very little protection for YOU.
In the end, there was no statistically significant difference between those who wore masks and those who did not when it came to being infected by COVID-19. Of those wearing masks, 1.8 percent caught COVID, compared to 2.1 percent of the control group. As a result, it seems that any effect masks have on preventing the spread of the disease in the community is small.
However, I fault the article for not saying anything about masks protecting OTHERS.
Thus, one needs to look at the Rt rate, which is rate that the virus is spreading. You can do your own analysis quite easily ... the easy answer is that most of the states with mask mandates have WORSE Rt measures than those without. This is especially interesting for states like Minnesota that have larger cities. It seems that Iowa and Minnesota would be good comparisons due to relative population density -- perhaps one can throw out states like South Dakota with low density, which obviously helps slow spread.
So why is MN worse than Iowa?
The bottom line is that at least mask MANDATES don't seem to be effective. Naturally you can find "studies" that are all over the board. My experience is that the Minnesota people are being very compliant with wearing the masks. If they work to prevent the spread, they ought to work in Minnesota!