Run this in the daughter's room where we always have bad air and feel dusty. After one day, there is already a difference, even though the sensor thought it was good air from the beginning. Think it is a very good product for the price. Above all, I like that it is networked and can be integrated with Home Assistant so you have full control and can control remotely without becoming dependent on the app from Xiaomi, even if it is completely ok. Unfortunately, the fan is not particularly quiet other than in the night mode, but then it hardly makes any difference. I have solved it with a motion sensor so if no one is in the room I set the speed manually and as soon as someone enters it goes to silent mode. At night I set it to idle mode. After driving for a few days, the room feels fresh all day.
Edit: have borrowed this now that the daughter is away and put it in the bedroom which was okay air before. According to. I have no major problems with the sensor, but the feeling is clear even after driving the auto mode for a few hours. However, this is during the high summer heat which is probably the "worst case" for me as a pollen allergy sufferer. Conclusion: will probably be enough to buy another one like this. A more advanced one, however, I have a hard time motivating.