Everyone not sick should be using Respirators classified as N95 / FFP2 / FFP3 or Half Mask with same class filters.
This DIY is suitable only for already sick.
If you're in a high risk group, you should absolutely be wearing a mask. Every high risk group prevention is potentially worth an ICU bed or a hospital admission slot.
I've ordered a bunch at about $0.50 and if I get the order, I'll be driving most of them over to one of the local hospitals in Seattle.