I have the PRVKE 21L backpack, which is great, but the internal organization of the DUO wins in my book. Even though the DUO is smaller, I find that I can carry more things more efficiently thanks to all the inside pockets. The PRVKE doesn't provide nice internal organization like the DUO, which means I often have to pile things on top of each other in one of the two compartments.
The pop-up cube on the DUO is such a great idea. The camera cube in the PRVKE is nice, but a bit stiff and bulky. The pop-up cube is perfect for the mirrorless kit I carry around while traveling, and still leaves significant room in the rest of the backpack to carry other things. The only thing that I prefer on my PRVKE are the straps, which are wider and sturdier, thus providing solid comfort. I noticed that my shoulders get tired faster with the DUO, but the DUO is still an ace pack!