I've used this pack for a couple of day hikes, to get used to it, and then a 2-day hike across the Bisti De-Na-Zin Wilderness in New Mexico. I carried 14 liters of water, which made up most of the weight - about 31 of the 48 pounds of payload at the start. There is no source of water in the badlands that make up the Wilderness area. This was a practice run for a future Grand Canyon trip.
The pack behaved very well. I found it easy to adjust the straps at loading and unloading. I am glad that the main straps hold by tension, not velcro. As my sweat moistened the webbing, I did need to make fairly frequent adjustments while walking, but not unreasonably often. Once my load shifted when my water bags slid to one side after a jump across a small gap. I was able to get the bag off and handle it - the waist belt was important to not tipping me over at that moment.
The design is very good. Its materials are sturdy and some weight is accepted for thick bottom material, strong zippers, etc. I found the loading system intuitive. Really appreciated the lower compartment for sleeping bag and pad. My only quibble with the design is that the side entry into the main compartment also doubles as the outside pocket to stash medium-size items. If the pack tips upside down, there is a gap at the top that allows those items to slip into the main compartment. IT would be less annoying if there was no such gap and a zipper could completely close the main compartment off.
I am 6'2" with short legs - the headrest in coach-class airline seats usually hits me between the upper shoulder blades. But the Large size is almost too big for me. On the shorter setting for the shoulder straps, the pack hits me just a hair below the right place. It works, and I did not have any problems, but maybe the Medium size would have been closer to a perfect fit.