While I don't use coffee hulls let me say this is that they are very dusty. At least initially when spreading them and possibly when the chickens scratch around. I think long term it is probably not good breathing the dust for humans or chickens. I have worked in the waste handling industry for 30 years and used to service a trash compaction unit from a coffee roaster. When it was dumped a cloud of brown would come out and you would have to wait to make sure the container was empty as you could not breath in the facility. It did make the waste facility smell great and absorbed a lot of water but sure hard to breathe in the building. I suppose it would be OK to use outdoors though, once it gets wet the smaller dust particles would be captured. IMHO