The market that these were designed for were the sniper community, guys who need to carry two primary weapons.

I haven't played with the bigger packs with rifle sleeves, but I have with the Halftrack and the Gun Slinger. On both backs there was ample room to lash stuff to the outside if needed. Both these packs had accommodations for hydration bladders (the Halftrack had hydration pockets on the side making it easy to access and add water without digging through all your stuff).

I never put these packs through there paces, just played with them and I plan on getting a Gun Slinger or smaller bag for a range/hunting backpack in the near future. One of the Halftrack packs I worked with had seen a tour in Afghanistan and was still 100% usable. The quality of these packs is on par with Eagle Industries, Kifaru and Mystery Ranch (you should look at Kifaru and Mystery Ranches offerings, outstanding rugged packs with lots of options to "customize").