That slide out tray is brilliant! I don't have a set up for it (I do have a tray with PDZ though and love it), but having a slide out without having to go inside is awesome.
Pooping on each other will not be good! I have 9 feet of roost for six birds so theoretically I could take the middle one out and still have 12" per bird. I wonder if the birds could reach the top roost without the middle one....