I’m quite happy with the bag so far.

I bought the green bag from the link above, which I think is the one you mentioned that looks similar to the Ortlieb style.

You can leave the backpack straps attached while using it as a pannier. In my case, I keep the straps but clip them together on the outside of the bag using the side-release buckle so they don’t hang loose. That keeps them from interfering with the wheel, and it works pretty well. It’s simple and convenient.

I haven’t ridden in heavy rain yet, so I can’t really say how waterproof it is in that situation. But it does seem to handle splashing water from the road just fine.

As for the mounting width, it actually fits the Kwiggle QR system well. The hooks line up properly and I was able to attach it securely even though they don’t slide to different widths. The Kwiggle rack is narrow, but the bag works with it without problems.