In decades of shooting I've never found the perfect camera pack. Shoulder bags, back packs, sling bags, they all have their uses but there are trade off with every one, and this pack is no different. I applaud Andy for creating another choice, but since I've never seen it, touched it, felt it, etc. I can only go by what I see/read on the site.
The pack is light, and we all want to carry less weight, so that's a welcome feature.
OK, it's big, but........ Do you always want to carry a 500/600 lens at the same time and little else? Where are the EXTERNAL pockets to hold all the other stuff like car keys, filters, pen/pencil, small flashlight for working in the early morning dark? Where are the attachment points to hold anything other than a tripod? No, I didn't forget the water bottle holder, it's just too limited to count for much.
Unfortunately it's extremely over priced (unless you're fortunate like MR who seems to never have a working budget or financial limitations). Alas, many can not say the same especially in this "economy" or whats left of it. Perhaps a more realistic price is $249. I'm not sure I understand the $399 with a "MSRP" of $429; where did that come from if you're the mfg?
I'd suggest anyone looking for a large airline travel bag to look at the Lowepro Vertex 300.... It's fully airline compatible with a pack/stow-away harness, it has many attachment points where you can add slip lock attachments for extra pouches when needed - and I often do. You can place the tripod on the front or either side, it has a fully adjustable harness (with more attachment points).I've hiked with the Vertex 300 fully loaded for hours (carrying 45 lbs/20 kg.) and it's extremely comfortable. I only had a 300 f/2.8 IS in there as the largest white, but also had 6-7 other lenses and gear. The downside is that the pack weighs more, but it also has a full padded laptop compartment for those that want to carry one (I wish this was removable). It easily holds MF and even LF gear too. The Vertex is extremely well built and seems a lot more flexible in all ways...
For a price comparison, the Vertex has the typically higher (insane) "retail" price but I paid $180 out the door - including tax - from a large retail camera chain here in Boston. That leaves you with a more flexible bag and $220+ to use as a down payment toward buying a sandwich and drink on the airline......