I've used this pack extensively on trail runs and a couple of rides in S. California. The fit is incredible and it is easy to forget that it is there. I particularly like how it sits high between the back of my shoulders rather than down low like a traditional pack. The quality of the construction is great and better than some of the pictures on the website suggest.
I find it has some shortcomings:
1) I like to eat "normal/real" food such as crackers, fruit, PB&Js when out for long runs rather than a bunch of pre-packaged "engineered nutrition" bars and gels. But these just get trashed and smashed in the pockets that sit on top of the shoulder (usually while taking in and out of the pocket). If using flasks in the front pockets the shoulder-top pockets are the only place to put food in reach while on the move.
2) the main body of the pack has very little room when using the 2L bladder. Any food you try to store is there will get smashed (see above) unless it is a bar or the like. And with a bladder there is barely room for a shell and some arm warmers. The add-on pocket sucks and just loosely flops around on back of the pack...but it was a nice idea. They make a 12L pack, but if they just added 1-2L to this it would be perfect.
3) for cycling, the pack sits way to high on the shoulders for my taste. When riding a bike, I'm much prefer a pack that was closer to my center of gravity rather up high on my shoulders. But that's a matter of personal preference. And…