Lots of room and waterproof compartments but hot and heavy. I have a lighter non-biking backpack I'll use in summer, sometimes carrying on my back, sometimes on my front rack. Sometimes I pull out the Ortleib panniers, but they don't play nice with the Salsa rear rack. The latches don't attach tightly to the tubing, so it bounces up and down and drives me crazy. The lower tab attachment wears away the metal on the rack. Been considering for about the last year the Porteur Bag that Velo-Orange makes for the front rack; but it has the drawback of not being as convenient as a backpack.
Then I started thinking I need to make a pouch out of frame bag material to carry a U-Lock and velcro it to the rear rack. That'd get some weight off. Then I looked at my Revelate Tangle bag I use for excursions or general mountain/road biking and thought…wait a minute. My medium size u-lock might fit in the deeper right side pocket. And so it does! Then I looked around some more and pulled out a handlebar bag from the basement bike stuff stash.
Look what came in the mail:
The Chrome Kadet
Almost sent it back because of the way it hangs diagonally on the back instead of lower like many messenger bags, and because it doesn't hold much more than the handlebar bag. But it's a nice lightweight well-made bag. I can wear it or carry it on the front rack. The Kadet is good for weekend rides around town, too.
So the Kadet/Tangle is my latest greatest commuting set-up. For now.