We're working out what we think - we'll add our view here!
Granite Gear says:
Never be without a backpack! This ultralight sil-nylon pack stuffs into a built in pocket (6” x 10” x 2.5”) that can be worn as a hip pack or tucked away inside your carry on. When you need extra capacity it unfolds into a full featured day pack. Padded shoulder straps (with ear bud garages) and adjustable sternum strap make the Go and Stow Travel Pack a comfortable way to carry the essentials.