Save your money on cheaper bags that claim to be water proof, they aren't, only Ortlieb will keep your stuff dry and preform like it says it will. Truly the gold standard. Amazing product!
Just took it on a 2-Day ride on the Katy Trail in Missouri. Check it out if you haven't been on this great trail and it is now linked to the Rock Island Trail. 267mi! After I figured out how to correctly tighten the straps, it was very secure and I hard noticed the pack behind me. I crammed a lot in there and didn't even max it out for a two day non-camping trip. There was no rain, but I felt comfortable with the quality of the material that my stuff would stay dry. I plan to add the front pack for a longer ride in the fall.
I have experimented with many bags over many years as a recreational and commuting. cyclist and the Banjo bag has proven to be the best of all in terms of size and attachment. Other bags invariably don't hang or fit right or are either too large or small. Banjo is just right