So I got the hay feeder yesterday and installed it.
What a clever, simple design ! It is sized to fit flakes of their small bunny bales (of which I bought 2 - very nice quality hay). I put their regular hay in it for now and they are loving it ! Very easy for them to access, but they can't make a mess with the hay. It was simple to install, and it's really cool how the wooden box snaps into the galvonized metal part. Very easy to use.