Comment by londons_explore

I wish analysis like this would stop using tests of the filter material to make any judgement about the purifier.

If the air passed through the filter precisely once and then ended up in your room, it would be valid. But it doesn't - the air passes many times through the filter, and mixes with the room air again and again each time.

That means it is far less important to get 99.9% filtration, and far more important to get more cubic feet passing through the filter each minute. That dramatically changes the optimal design.

To see why, imagine a room of 1000 cubic feet. Now filter one of those cubic feet, and put it back into the same room. A good 99.9% filter has just removed 0.0999% of the dirt. A bad 90% filter with double the airflow removed 0.18% of the dirt. The bad filter is much better!