I used to wear my messenger bag very low, still do on the rare occasions I'm not using a rack / panniers. I find no difference in the comfort of it high or low, other than sweat in the summer. I HATE wearing a backpack while riding because of the extra sweat. Messenger-high is slightly better but not great. (I have the large PVC North Face bag). Messenger-low is OK. A heavy load I'll put in the small of my back, a light load maybe even a little lower. I guess my butt doesn't sweat as much as my back - perhaps a blessing?

Low down I can swing it around all I want to. May have to loosen the hip strap, but not the shoulder strap. Which is fine with me, because I haven't mastered one-handed operation with it. Thanks for those vids.