Specification
Model: NS-PRO1M
Material: Fiber+Nylon
Color: Black
Net Weight: 263g
Dimension: 390x110x10mm(Shoulder Pad)

Q&A

Q1: Can someone explain the definitive purpose of the strap that goes under the arm? Like, have you had a real world situation where it helped?

A1: I place the camera somewhat behind me using the two clips at the bottom. Without the strap under the arm, the shoulder pad tends to slip off my shoulder since I have a bit more weight on the back of the strap. My wife didn't like the under-arm strap, so we took it off.

A2: It keeps the main strap from pressing up against your neck. After using it for a couple of months, I love it.

Q2: I have a mirrorless camera. Is this strap overkill?

A3: I wouldn't say this strap is overkill. It's all about convenience and comfort. Even someone with a point-and-shoot could use this strap if they're going to be doing a lot of shooting in a day. It just depends on your preference. I didn't like having my camera hanging around my neck with the standard strap; over time my neck and shoulders would start to ache and I found myself fumbling around when trying to get my camera up and ready quickly. With this sling style strap, I literally just reach my right hand down and it grabs the camera in the same position I will be holding it when I bring it up to shoot. Up to you, but at this price point, it may be worth getting even if you only use it occasionally.