Yes, almost all websites give the filter "square footage" at a measly 1 air change per hour. So essentially they take the CADR, divide it by the (assumed) heigh

Yes, almost all websites give the filter "square footage" at a measly 1 air change per hour. So essentially they take the CADR, divide it by the (assumed) height of the room, and that's the square footage or square meters. Very flawed methodology! Typically for respiratory pathogens you want to shoot for 6+ ACH, so as a very rough initial guess I often simply divide the rated area by 10. And yes, every manufacturer only gives specs for the highest fan setting. This is misleading because typically this fan setting is very loud, so few people actually run it 24/7 (and those who do will probably suffer hearing loss).