I LOVE this piece of gear. It is my absolute favorite right now, and I take it on any ride over 10 miles.
It is so well designed that I can easily carry a U Lock without feeling like the weight of that plus the 3L of water disturbs me very much. It breathes very well, and the overflow capacity is INCREDIBLE! I can take this little guy on an overnight summer backpacking trip no problem!
If there could be one more feature on the bag, I'd advocate for soft side pockets on the main compartment just for another snack or two, but for now I make the most out of the hip belt pockets.