The following are first, and by no means definitive, thoughts. A complete version will be in the review article which should see light at the very end of the year.
The Evolution is an external frame pack. An updated, very modern one, but it has a lot in common with the Trailwise hanging on display in my garage. The mechanics of the harness attachment and the very clever articulating frame seem to have largely tamed the renowned external lurch. I'm hoping snow comes early so I can take it skiing before the article is finished and give it the definitive workout in this respect.
That articulating frame works via a press-fit joint in the middle of the bottom of the frame. The upper ends of the U fit into a fabric sleeve, which holds tension between the two and has a slot for a carbon tube which provides additional support. The lighter the load, the less tension is placed on that upper assemblage, and the more the joint is free to move, allowing each half of the frame to move independently. Increase the load, and tension on the U increases, stiffening up the whole rig. None of this effects vertical stiffness, which seems to be effectively unlimited. Greater lateral stiffness in the frame is good because it keeps heavy loads tamed. I was skeptical of the initial claims about this feature, and have to report that it works as advertised. Very impressive. My only concern is long-term flexion in that joint eventually producing play.
The hipbelt is stellar. I don't have much in the way of a butt or hips, and as a result have always struggled with bruised hips and the need to cinch the belts on internals, which rely on lumbar pads, very tight at heavier loads. The Evo hipbelt just sucks into my lumbar and stays put with modest belt tension. I haven't given it a sustained workout at very high loads, but will soon, and today see no reason to expect problems.
The shoulder harness is good, but hasn't blown me away yet. It seems a bit narrow, and the curve a bit off for my shoulders, but his opinion might change with more hours under load.
All the components I'm testing come it at or below claimed weight.
Construction quality is excellent.
A lot of the details which went into the Evo frame will be irrelevant for 95% of BPLers 98% of the time. At 40 pounds and below, proper torso length, stays, and a good belt and shoulder straps should have no issue getting the job done. Some of you want the ability to carry weights above that in a manner where the pack itself isn't contributing to the fatigue factor. The Evo frame is worth a look.
