60+ years of hunting, 15+ years of Hunter Ed, and I bought one of these (then called "Boonie Packer") when they first came out (15?? 25??) years ago. I will never recommend one of these, first rule in my book (well, second --- treat every gun as if it is always loaded is first) is, muzzle in a safe direction. If you use this sling as a way to have hands free for other purposes, the gun is able to swing fairly freely from side to side, and could slide muzzle up or down if you lose your balance, could also contact ground, mud, snow, etc.
I used it a few times, but stopped after an incident while hunting in a group of three. Shin-deep snow, snow-covered brush, varying distances between us, and a .338 with a tang safety that somehow got bumped off. I don't know how long I carried it that way, at least several minutes. I still get the shivers when I describe it to the kids. Now that sling is on a retired stock, with a spotting scope mounted on it as a novelty. The "barrel" is a length of electrical cable fastened in the channel and twisted into a corkscrew and the trigger is the all-thread that secures the scope. So I guess you could say I'm still using it..... but it'll never be used on anything that goes "bang!!"
Flame me if you like, but that's where I'm staying. I will say, it's fast to put into action, if you're ready, think about what you're doing and it's adjusted properly.
Edit to add: Per Dr T, I have three of the Montana Slings and luv 'em!
