I get the fat free feta from Trader Joe's and I like it fine. I don't know if I would use it in say, a feta cheese sauce or any dish where feta was the primary flavor. I think the ff works for me okay as an accent flavor. It is milder that feta and not as rich, but it works for me.
Of course I do okay with lots of fat free products such as the cream cheese and sour cream, so take my opinion with a grain of salt!