This is exactly what I was looking for!
- Quick and safe mount without extra hardware. The bag has a "pocket" which hooks on a plate on the tail of the bike above the tail light. The straps then get looped over the passenger footpegs. The bag stays put and it doesn't need any extra hardware.
- The right size. The bag fits 16' laptop and a change of clothes easily in its collapsed form. Perfect for having all the things in a backpack and keep it on the bike.
- Doubles as a backpack. It's decent as a backpack, but it's good enough to get off the bike and carry comfortably around for commute or doing chores.
The bag has a single volume, it doesn't have dividers or anything. Which makes it versatile but also you'll have to keep it organized yourself. It has an external pocket (visible on stock images) and internal pocket with mesh on the "lid". When you carry the bag as a backpack, then it tapers down which looks a bit funky, but it doesn't affect functionality too much. The opening is on the top, and it has limiters, so if you open then bag when it's positioned vertically, then the "lid" doesn't fall down.
Overall, I'm very happy with the bag, how it fits on the bike, and comfortable with it in the backpack form.