The thing you have to remember with millet is it has a very fast decomposition rate...ie..rot. Tnduckman is correct though, birds like it, but a lot of times there not in there for the millet itself. With the thick vegetation that millet produces, its ideal for all the microorganisms (insects, plankton types)that ducks love during warmer times when "hot foods", such as corn and milo are not favored.
I've hunted swamps where guys threw out 50lbs of millet in a swamp in June/july over 1/4 acre opening. They killed ducks all season, but they hunted it sparingly. Warmer than average winters and early season, ducks will tear it up. Extremely cold season....not so much. But nowadays, its about impossible to guess what the winters are gonna be like.