There doesn't need to be tests on humans. We have plenty of research showing that viruses harm humans as do small particles in the air this isn't in question at all. These devices have been shown to remove these items from the air using engineering testing based on physics like the electrostatic force and the laws of motion. That they work is not in question, they do filter the air.

The only remaining aspect is how well do they clear air that is constantly getting dirty that has been tested as well, for the most part 6 air changes an hour seems to drastically reduce the particle count.

The problem with medical research "questions" on filtration currently is it thinks random control trials are the gold standard of proof. They aren't physics and engineering tests are a much higher quality of science and evidence. Filters work, respirators do work to remove viruses because we know the size of aerosol they tend to live in (1-5 microns mostly for something like Covid) and how effective the filters are at those particle sizes.