If you go DAA, and want to use it as a backpack without a cart, DO NOT - repeat - DO NOT get the large. It's a PITA to carry as a backpack, too tall & hits/rests on my mag pouches while carrying & can get loaded down/too heavy very quickly.
If I were to do it over again, I'd go DAA medium all day. Heck I might just sell the Pro and do that anyway.