This is an interesting website.

https://smartairfilters.com/en/blog/how-to-...y-air-purifier/


You dont need expensie filtration nor junk like xiaomi.

Xiaomi air purifier 2 is famous for junk product.

https://smartairfilters.com/en/blog/xiaomi-...ntrol-purifier/

https://smartairfilters.com/en/blog/xiaomi-...nsafe-86-hours/

Yeah yeah. People said Purifier 2 and 2s is different.
Bear in mind 2s is just 2 with OLED PM2.5 display (might be inaccurate as well as they are famous for rigged readings)

If he is biased he could mention particular brand instead.
Or selling his own brand.

The kind of DIY looks ugly but from his test it looks the most cost effective