That may be your experience and I'm happy for you, but your statement is not universally true. I know exactly how to use these panniers. On separate occasions both the "button type thing" and the "plastic knob" broke (rather, the cheap integrated hardware broke) during commutes.
As I said, I still use them daily, but I wouldn't recommend them to someone who hasn't plopped down their money yet. However, these are the only panniers I've ever owned. To the extent that their attachment and removal is uniquely simple, I'll admit that's another check in the PROS column.
Well yes, if they break I suppose they come off. My comments were directed at the person I quoted, who seemed to think that they can fly off if you simply bump them.
Mine have never broken, so I recommend them.
Yours broke, so you don't recommend them.