Literally useless.
Yep...seriously i'm doing that with the Samsung AX40. PC Room too small, not that I could help it.

(Sharp 840 is in MBR).
Doors opened, windows closed. Ok lah. I have a PM2.5 monitor, it does show even on Sunday's AQI 300 that it's working a-ok at all parts of the room. Great. The "leak" is not that jialuck. The levels did go down with the purifier working hard.
But windows opened and doors closed is a very different scenario liao.
Reduce AC use lah....don't wanna waste money, 24/7 can die man.