The iCloud Drive file picker in iOS 10 really hard to use to save a file, it currently shows all your folders in an exploded view in one long list. This view really needs a search, and view modes like the finder, column, list, and icon. I've filled a radar and feedback but I'm afraid it will end up shipping in this form and it makes iCloud Drive slow and hard to use. It looks like this, http://cl.ly/hDkF