After almost 40 years of using this type holster
Shoulder holster/upside down, I prefer it to every other one that I own. I can shoot a man attacking me from behind without having to get him off my back. I turn my body to align it with the target thereby reducing the mass area for the other person to aim at. My problem with hip holsters is that if someone knows you have it on and have practiced for just 15 minutes, they can disarm you before you know it. I'm not saying they would have their hands properly aligned to use your weapon quickly but they can throw your weapon away from the immediate area thereby preventing you from using it. That is not the case with the holster I prefer.
I also use a shoulder holster with horizontal carry (Miami II Harness). However, I do so realizing that it has limitations (as do all holsters). I would recommend using this holster with a double action, but I would not want to be around anyone using this type of holster with a cocked single action.