I'm running two HST slings (pre-Specter, these are CQB Solutions models) & I've been very satisfied with them. Like any single-point, I wouldn't want to have to carry a rifle with them on a long patrol, but for what I use them for (entries, high risk apprehension, etc) I don't usually have to carry the rifle more than a couple of hours, so they work fine.
They are great for building clearing, if you prefer cross-shoulder transitions on corners to doing everything from your strong side.
Like all the single-points I have tried, you have to be conscious of using the support hand to swing the rifle out of the way when transitioning to handgun. With the sling over my strong-side shoulder, if I just drop the rifle, it has an annoying habit of hitting me in the family jewels about half the time. So I just use the support hand on the forearm to swing the rifle over to the support side while I clear my handgun with my strong hand.
Also if you go to prone or kneeling, you have to be careful to keep one hand on the rifle, to avoid having the muzzle dropping into the dirt.
Overall, I really like the HST. It has worked well for me so far....
ETA: I tried putting the sling on top of my support side shoulder instead, to avoid hitting Captain Happy & his friends, but when I drop it, it has a tendency to swing over in front of my holster & get in the way on transitioning to handgun. So I went back to the original carry, & just train to control the rifle with support hand until it's out of the way.