Since this describes such a different experience from my sibling comment, I'll have to add that my purifier cleans particulates just fine (close to 0 µg/m³ in summer and 20-40 µg/m³ in winter), which is supported by three separate PMS5003 and a couple of years of data piped into Grafana.

I don't know why it's so useless against dust. Maybe we have more coarse-grained dust which quickly falls down on the ground.

The blu air filter has a prefilter specifically for dust and it gets filthy. That has to get washed in the laundry regularly. Maybe some combination of that, it's cfm's and placement might make a difference?

I have 2 coway units in a ~800sqft apartment and still have tons of dust but I open the windows a lot when its not smoky and I have a dog so who knows. The pre-filter does trap a lot of dust so there is obviously some (maybe minor) reduction.