I really think different things work for different situations. I love my system of pine chips and mulch outside. Works for me and for my girls! That's all that matters :-)
You might have to clean more often seeing how they don't free range...and keep that moisture out of coop. Just have to keep researching different methods and see what's best for you n the girls!!
They don't have an enclosed outside run? I personally use shavings in spring/summer and when it's colder I use hay. But everyone does it differently! They love to pick the treats out from the hay n shavings!