Liability. Tell people that makeshift masks offer coronavirus protection, and hear the class action lawyers sharpening their quills from a hundred miles. Even if the masks, deployed at scale, help reduce the R factor.

Just have employees sign a waiver.

That's a good point. To complete: Just tell CDC to tell employers to have employees sign a waver.

The link you posted is commercial (selling air filters), better to link to the original study from which this is based:

https://www.researchgate.net/publication/258525804_Testing_t...