So, I often like a sling-style strap so the camera hangs off to the side, out of the way, and easier to conceal inside a jacket. Of course, you can do that with the conventional way by just putting one arm inside the strap loop. However, I also love to use the wrist strap with the M9, so I need to be able to disconnect the camera from the neck/sling strap. In fact, most of the time when I'm walking about, I have the wrist strap on and the camera on my right hand so I'm ready to catch the decisive moment.
The wrist strap use up one side, and leave the other side for my sling-style strap. I found the OP/TECH USA quick disconnect camera strap connectors to be very versatile. Since it's just a thin nylon string and the M9 is quite heavy, I double it up and it doesn't make it that much more difficult to attach or disconnect. Here's a more close-up image: