I have a Banjo Bros commuter backpack and I strongly considered the Ortlieb Messenger Backpack before getting it. The basic advantage to Banjo Bros vs Ortlieb is price and in some cases design. Ortlieb wins on materials.

The Banjo Bros commuter backpack has more places to put things than the Ortlieb pack and the way they did the roll top minimizes the "wings" that obstruct rear view on the Ortlieb and other similar backpacks.

This doesn't apply to panniers of course but I think it helps to differentiate the products of the respective companies. Banjo Bros is more budget minded and has some clever design features relative to Ortlieb. They also include some accessories that Ortlieb will charge extra for. In overall quality however Ortlieb makes a better product.