The only profile I really see an appropriate application for the single-point sling is inside the car, but since that usually involves getting in and out of the car, then I personally don't have any use for them. On deployments or training exercises, everyone I have seen that used a single point was always knocking their knees, spinning the carbine around, muzzle-striking the dirt, and butt-stroking their face inadvertently. They are one of the most problematic sling designs for real-world use, but do have some benefits for an under-the-coat gun. I still prefer a bungee figure 8 for under-coat guns, but that's pretty old school as well.
VTAC slings forced me to stop making my own personal slings back in the day, but I also have the Vickers, and an Ares Armor quick-adjust 2-point that I just started using in cold weather. I got it from the prize table at Sniper Adventure Challenge this year, and seems to be very similar to the Vickers sling, but uses a loop instead of a pull tab.
I use the VTAC as a patrol sling, assault sling, and shooting sling all in one. The ability to lock into a super-tight shooting position no matter what you are wearing is a big plus with the VTAC.
