My daughter got me one for Christmas (I'm amazed she found it on her own). I haven't used it yet, but packed for my first solo trip (in my Sawyer Autumn Mist). It has great capacity; I easily fit all my shoulder season gear and clothing in it, including hot tent gear/stove. Inside each section is one large pocket. I have RBW liners that I use with other packs; they can be used, but as you probably know, they are for top loading packs so the fit isn't clean. I think RBW should design some liners to fit specifically for this pack.
The pack is pretty straight forward; I easily figured out how to separate the two parts and put them back together. In my Sawyer, if the pack is fully loaded, there is no way to keep the two sections together and have them fit in the bow or stern of the boat. I could put both sections behind the seat (one crosswise and the other parallel to the centerline or I could put one section in the front and one in back (both parallel to the centerline). Next month, after I uncover the canoe, I will try the two different configurations to see how it works best with the barrel and other gear. I don't have a tandem boat, but I'm quite certain the pack could be put amidships with both sections together.
The shoulder straps and back padding on the pack are just as Andy describes it - substantial and very comfortable.
I already had a tump line from RBW, so I am able to use that with the pack. There are lots of daisy chains for securing things to the outside of it. Unfortunately, there was nothing in design to allow for their large external pouch to be attached to it. I did jerry-rig connecting it on the side and on top with lashing straps, but the pouch doesn't clip-on as cleanly as it does on the barrel. I'll be experimenting with securing other items, such as my thwart bag, PFD etc to pack with the daisy chains.
There are pleny of grab handles on the pack, which make it easy to take in and out of the canoe. Personally, I probably wouldn't use this pack on a trip with long carries. I have a Granite Gear Portage Pack system with a clip-on thwart bag and mesh bag that works much better for those trips. I anticipate using this pack when on trips with no carries or short ones. If I have the two sections separated, it would be easy enough to just pick each section up by the handles and carry it up to the campsite or once arriving at the carry, I could take the two sections out, spend a minute or two putting them together and then doing the carry. Of course, if using a cart, I could probably keep the two sections in the canoe when doing the carry.
Overall, I'm impressed with the pack and look forward to using it on some of my trips; the first test will probably be on a trip to the Bog River/Lows Lake in the Adirondacks this spring. The design and the quality of the workmanship is what one would expect from RBW. I think with the addition of a clip-on system for the external pouch and liners designed for the pack, it would be an outstanding system for both solo and tandem tripping.