I've used one for years and really like it, but there are some issues with them.
You really need to watch your muzzle with those slings; they're best if you hunt alone. The muzzle is swinging all over the place when you don't keep one hand on the forend.
They don't work well if you wear a pack. The pack will get in the way of the sling and prevent it from sliding over your shoulder.
It can put the rifle in a position to hit anything else you carry depending on your physical build and height. If you carry your binos on your chest, they may hit the scope on the rifle. If you carry a sidearm on your belt it will hit the gun. If you carry a knife in your right front pocket, the knife clip will hit the gun. If you have a hip belt on your pack, it will rub on the gun.
They work ok with a heavy gun, but they're not as easy to just alternate shoulders to switch between your left and right side as a more conventional sling. If a safari sling is adjust properly it will hang different depending on whether you're left or right handed.