The angle closest to your feet provides clearance for your heels and lower legs, which is vitally important when paddling in soft sand/dirt or when, inevitably, you have occasional offs. Many adventure motorcyclists, including Ted Simon most famously, have broken legs because they were using non-Jesse panniers with square rather than angled corners. Our panniers also feature side angles for improved cornering clearance.
Box rigidity is the second reason for angled corners. Imagine the difference between trying to push in the corner of a cardboard box versus the side. You know you can indent the side of the box with much less force than the corner. The same holds true for aluminum (aluminium) panniers. Our boxes have been crash-tested by many customers, who consistently tell us how surprised they are that our products survived with so little damage.
There are two locks/handles per pannier and one on a top-box, with a single key that locks everything.