I live in the country, no bad air outside, but I have noticed a deduction in the dander, and the air just seems cleaner inside. My son has asthma and after putting them thru my house and each kid had one in their bedroom, he rarely had any asthma problems. I have on in my bedroom next to Talons sleep cage, and when I vacuum the filter once a week, it is covered in bird dander.
I had bought the ones that were advertised in Bird Talk for many years. But I know they don't have a very good business reputation. JWR Germicidal Bird Systems is the brand. I don't know if they sell them anymore, but I have a lifetime supply of filters and bulbs. They come with a filter than can be vacuumed and washed as well as a germicidal bulb. I run them 24/7.