This. How do you harvest/refresh the compost though? Just move the cage over? Do you kind of suspend the cage a bit and let the little stuff fall through?
For me we have a coop and then a fenced in run which is relatively large. I built my gate so I can fit a wheelbarrow inside. I just shovel some out and smooth out the pits I've made. The ground doesn't need to be perfect because the chickens will always be making more compost and shuffling it around. If you had a smaller setup, I'd think a mobile coop & mobile run would serve you really well.