Not OP but I've also researched this topic and settled on an iqair filter back when I lived in China. I did borrow a particle monitor and the drop in the number

Not OP but I've also researched this topic and settled on an iqair filter back when I lived in China. I did borrow a particle monitor and the drop in the number of particle was flagrant when turning it on. Subjectively it also did a lot to improve the air in the house... I'm not sure that something like an iqair is needed in a place that isn't as polluted as China (we sold our air filter when we moved out)