Ortlieb sets the standard for bike touring gear. Construction is superb and it is totally waterproof.
While this bag is designed (and likely ideal) for touring, I use it for commuting. It carries a ton of stuff with space left over (I just use a single bag). It easily swallows my 15" laptop in a sleeve, change of clothes and lunch. All in all, it weighs about 20 lbs when full and it is solid.I love that this bag has one main compartment and that you can over stuff it. Very user friendly, versatile and accommodating.
The rack attachment system highly adjustable (very well thought out), so it should attach to any rack just fine. Once or twice the lower arm that holds the bottom of the back to the rack had enough give that the back would swing loose on inside turns... but the top was attached to my rack securely and it was at least partial user error for not getting the bottom attachment rack snugged up to the rack. Still, the bottom plastic arm could be a little thicker/stronger to avoid this. But all in all, very minor.
My biggest complaint is that this bag doesn't have more and better external pockets. It does have one front pocket which is okay, but not great. First the pocket width tapers, which is annoying. Second, the pocket doesn't have a zipper, but instead closes with tension from side straps when the bag is full. And when the bag is full, the pocket closes securely; when the bag is mostly empty, this pocket doesn't stay closed very well... if they don't want a zipper on this pocket, at least add a couple of snaps or a magnet or something to keep this thing closed.
Speaking of pockets, I wish this had more! Ideally they'd have them externally, but internally under the "hood" over the top would be cool too. There is no easy place to stash your wallet, phone, keys and other commuter essentials. I have the one front pocket full with my basic bike tools -- and due to the lack of a zipper, I just don't trust it to hold my wallet, keys or phone. There is a small mesh zipper pocket inside the bag with a thin paper/map holder, but these pockets/sleeves aren't that accessible when the bag is full and closed. And yes, Ortlieb sells an extra pocket I could attach to this (and I still may), but I don't trust myself to attach it correctly while keeping this bag waterproof. Plus, I'd like some small internal hooks to attach my laptop sleeve, but that is nit picky. In fairness to Ortlieb, this back was not designed for commuting; it was designed for touring. I am guessing for tours, the quick/easy access pockets aren't as necessary as they are for commuting.
And Ortlieb does make a commuter specific bag with lots of cool commuter friendly amenities, but that bag is just too small to accommodate a change of clothes plus lunch plus a computer (at least for me).
I'd definitely recommend this bag; especially for touring. Plus, now that I have this bag (set), it is one less excuse for putting off that bike tour I have always wanted to do!