air ionizer, favorite or least favorite?

do you have an air ionizer purifier at home or work? what is your opinion of it and what model do you have, I have seen some that makes the air so clean and crisp it was great but others did nothin you could not tell you even had one running, unfortunatly I don't know the brand names of either, just know I want to get one for my apartment but also don't want to waste money, thanks in advance