We tried one of those, with the
chicken nipple on the bottom. It works well for the
chickens that can figure out how to use it. Training them is a bit of a pain, but once they know how it works fine.
You do need to make sure stuff doesn't get inside the
bucket, like leaves dropping from nearby
trees. Also important to make sure they don't perch on it and thus get feathers or
poop in it. The one pictured looks like they'd love to perch on it.