The "science" would indicate that their safety would be equivalent to you wearing a mask if they put on a second mask...
I ‘loved’ the one a couple of weeks ago where some ‘old broad’ giving me the evil eye while in checkout line (I was about 10-15 feet away) and she sneezed, coughed and hacked with mask firmly in place.
I thanked her for ‘protecting’ me and happy breathing.
The clerk was stifling a laugh while I left and the ‘old broad’ had plenty of space around her....
Then the other day I was at drive up window and some ‘old broad’ was standing there waiting and had the mask under her chin and when the teller came back to the window the woman PUT ON HER MASK to communicate between the window and the teller inside.
As she left she was pulling her mask down.
Some things there are ‘no words’ for. At least polite ones.
Do your own thing - if you must - but don’t give ME a rough time when I don’t ‘play your silly games’.