Um... it does have a shoulder strap. Thats why its a shoulder bag.
Maybe you missed that part of my post.
How is it useless for shooting? Why wouldn't you be able to hold the bag and the camera at the same time and you would the lowerpro? The Billingham bag is widely regarded as one of the best and most functional makers of finer camera bags out there. They were one of the first companies to ever make a soft bag.
I cannot imagine spending several hours walking around with a strap that only goes over one shoulder. Good camera equipment is heavy. It's one thing if you have a plastic prosumer camera and kit lenses, but good glass is heavy. Not to mention, i've owned a messenger bag in the past, and it bounces around on you in a way that's really annoying. I just find it completely uncomfortable. I'd rather look like a tourist than be uncomfortable all day. Maybe if I had meatier shoulders I would feel differently, but even the current weight of equipment in my LowePro is annoying. Besides, I'm really not concerned with looking styling when i go out with my camera. I don't wear my good clothes because the rub of the bags creates too much wear.
And to address your other question about fumbling around, the LowePros are compartmentalized.