Quote Originally Posted by opie View Post
Does the half hitch allow one to slide the knot and have it tension under load?
yep, it works exactly the same way.
I also dont see how anyone could see this as a stopper knot...
What that link calls a stopper is not what I am talking about. A stopper is three or more round turns with a half hitch on the other side. The standing part pulls back against the round turns, just like the Tarbuck knot. They only differ in the finishing hitch.

The classic use of a stopper is with nippers, which are small lines used to pull in a large cable, or hawser, aboard a sailing ship. The cable was too large to go around the capstan, being several inches in diameter, so they used smaller lines called nippers, only a couple of inches in diameter, attached to the cable using a stopper knot.