I've used various leather and padded fabric slings for almost 50 years of Western and international hunting. They all want to slide off my shoulder.
Last week I went to the International Sportsmen's Expo in Denver and bought one of those thermoplastic rubber "Ultimate Slings" from Specialty Outdoor Products. So far, just walking around the house wearing several of my different hunting coats, there isn't any slippage on my shoulder.
If it works, it works. Folks have preferences.
Which is why I use the boonie packer/safari sling - it CAN be slung from one shoulder, but is best used cross chest. Handy if wearing a pack, or using your hands for climbing, walking sticks, and best of all, using binocs without having to put the rifle down, danger of shoulder slippage, etc. Nor does one have to take the sling off the shoulder to shoot.
3 moose back, I rounded a spruce to see a bull with his nose down in my back trail. Maybe- maybe- 3 seconds later he was on the ground. That included 3 ways of confirming his slot-limit size. Eyeballed, ear-length comparison, and brow tine configuration - the latter of which was in error, as he had a double set of tines
Ditto two moose back. Last moose was taken from my snow machine seat. Both of which were "antlered moose" - no slot limit.
On the snow machine or ATV, I carry the rifle slung (boonie packer) across my chest, rather than side or hip carried while packing or walking. Keeps it from getting beat up. Much.
PS edit: I have a couple leather military slings - very good for shooting supprt. Also several different models of other slings. All of them in a drawer.
I'm still thinking about this one, that came with the rifle, but It's probably going to be replaced with a boonie-packer also. Any one know what it is?