Climate makes a big difference, and a covered run or greenhouse also makes an enormous difference.I have 2 cubes and one go up....For those thinking that there just isn’t enough space inside them, I disagree...During the winter they have the greenhouse to hang out in when the weather is terrible....I live in the Pacific Northwest in Washington.
If the chickens need to spend all day in a sheltered coop, the "coop" part of an eglu is NOT big enough. But for the way your chickens use it, the amount of space is fine, because they do not need to stay inside while they are awake.