While these units can range from 300 Rm to 2500 RM based on the different functionalities, i use one in the bedroom at night while sleeping and I can say for a fact that these air filtration units (the good one's) do make a difference.
I used to wakeup in the morning with a stuffed up nose and a face that seemed to be dirty, now I awake fresh , clean nose and face, I actually look younger.

I personally use the Sharp filtration unit in my room and I never had any problems for the past 4 years.