never seen one of these...

You dial in the advance or retard you want and as the engine speed increases, the drag overcomes the spring and the cam timing changes. Dad used to run a bigger cam and ran the timing advanced and as you raced, it retarded back to where you set it. It obviously is dependent very much on valve spring tension and anything that loads the cam. These used to cost more than camshafts in the late 50s and 60s so they never likely sold as well but they were a brilliant design that as you just said, were technology we are just now seeing.
His Rhoads lifters accomplish the same thing, sort of, using a different way to get there.