I wonder about the "minimum 4.8 ACH" thing. In order to get 4.8 ACH/h, most people would need big units on maximum speed. Or most people are using medium-sized units for medium spaces, getting 2-3 ACH, and most are happy with the results (online reviews).
I talked with two sellers in stores, and they told me that "on automatic, the purifier will clean the air, and once it's cleaned, will go on a slower mode". So once the air is clean (low PM2.5 count), there is no point for the unit to run at the same intensity as when it was cleaning the air. I understand air gets polluted again, but not at the same speed as the unit cleaned it (at least for low-pollution environements). But I hear and read from experts that "you need at least 3 ACH, preferably 4-5, and the machine needs to run 24/7".
There are many well-known brands with medium units of 250-300M3 CADR (147-176 CFM), rated for 50-80M2 (538-861 sqft), like the Philips 1000 series and the Philips Mini 900, with people using in rooms at these sizes, and being happy with the results (see online reviews).