I agree with you on the paracord sling. My son made it for me and grabbed the rings off of the mauser thinking they are all the same. Most of my sling clips are the standard pin type. This one has a quick release with a ball detentes. Kind of like a QR hose connector. The orange looks bad in the pick..
I am not sure what you mean by the thumb cutout. On the left side of the action there is a section of the receiver cutout. If you notice the SS pin in front of the trigger guard my father made a quick release to drop the magazine bottom. That way you dont have to cycle the unused cartridges out.
Concentrated power is not rendered harmless by the good intentions of those who create it.