Good until it broke...
I took this on a 3-day trip into the Grand Canyon--nothing crazy strenuous, 2 nights at Bright Angel. Down on day 1, fool around to Ribbon Falls on day 2, out on day 3. It broke on day 2.
By broke, I mean the center aluminum stay snapped about 1/3 of the way up from the base. I carried about 40 or so pounds into the canyon (adding a few on the way to help my wife's knees), and carried between 35 and 40 on the way out. The day it snapped, I was cinching the (seemingly nice) compression system down for the day trip to the falls. I imagine the problem had something to do with the hollow nature of the stay.
I did a lot of research and tried on at least a dozen packs before settling on the Z55, and, despite its weight, the suspension seemed capable, even resilient. I needed something that could handle a few days weight plus a DSLR system (camera, extra lens, tripod, etc.--nothing too fancy). Turns out it wasn't as strong as I thought.