Hi Momo,
I use FF in the summer, it doesn't work for me well in the winter with my work schedule and cold notherrn minnesota weather. I know some who use FF even in the winter with heated dog bowls.
I have never heard anyone say anything but good things about the positive outcomes for the chickens - they seem more eager to eat, feather faster and better, weight gain is fine, eat less....only negative I have heard anyone discuss is that the ff can be messy for the chickens, and some folks seem to be bothered by the smell. The smell is just fine to me - it is not a spoiled smell, more of a fermented smell. Oh yeah, some complain about the mess in their house or garage or wherever they are making the ff.
You need a tiny bit of extra time and space compared to dry feed.
I'm starting my ff up again.
Overall, cost is less even with additions because they are eating less , at least that is my thought. Harder for me to judge since in the summer they also eat less because there is more to forage than in winter.