I love doing FF. Sometimes I get lazy and fail to restart the ferment, so I keep regular store feed on hand. I use a 5 gal plastic food grade bucket, and cover with a lid that I push to seal on part of most of the bucket, so it's basically covered but not enough for pressure to build up. I use a base of whole oats, wheat, barley, and sometimes corn. I often add a handful or two of alfalfa pellets, and soybean meal if I'm going for higher protein. I've started adding a vitamin top dressing and powder as well. I've not had good luck fermenting feed pellets and the like, so I tend to feed those as-is.
For starters I've used whey (leftover from yogurt making), kombucha, and water kefir. The ducks seem to favour the ferments started with whey, but they are happy to chow down on any of them. With enough starter I can get some lively fermentation with plenty of bubbles even within 24 hours in my cool house.
I wouldn't say I save any money fermenting the feed, but I enjoy it from a mad scientist perspective, and I have noticed positive benefits in the flock when I feed it. Even my highly skeptical roommate agrees wholeheartedly that it practically eliminates the smell of the duck poop. That alone makes it worthwhile!