Lots of us use them. I just got one. Works great. I love it. I don't think the birds even notice it but I'm sure they benefit from breathing cleaner air.
U2-Poppy(Poppy lives with her new mommy, Misty now) CAG-Jack, YNA, Bingo, Budgie-Piper, Cockatiel-Sweet Pea Quakers-Harry, Sammy, Wilson ***Zeke (quaker) Twinkle (budgie) forever in our hearts
I use an air purifier and yes it makes a difference, as do frequent baths and clean cages. I'm sure my birds appreciate the clean air and the noise doesn't seem to bother them.
I also run one in each bird room, and it makes such a difference! my hubby turned one off while cleaning the room on Sunday, and I could not believe all the dander flying around that evening before we realized it was off.