Well I had my first hairball from either of mine the other day after well over a year of them moving in. Indoor only cats, and the amount of underfur that comes off them daily makes me surprised they aren't bald yet!
I feed them mostly indoor cat kibble (plus wet), which is partially anti-hairball formulated along with being lower energy, and a couple of times a week I put out a bowl of special anti-hairball kibble. As I said, only 1 hairball between them in 14 months - though I do notice that quite often their poo is sort of strung together by hair (yuk) which my DSis with indoor/outdoor cats has never seen in hers. So i reckon it does seem to work at least to some extent.