It's yet another old technique dressed up as a new fangled scientific discovery.
The funny thing is, if you trained the entire body 3 X's a week -- the way they used to say to train back in the 1940's, or the way you may have trained when you first started -- you'd essentially be doing HST. This is the way Steeve Reeves trained his whole life. I wrote an article called "Rebound Training" which applies the same principles.
So yeah, it's a gimmick, but it's a gimminck that works. EVERYTHING works. And everything stops working. That's why it's good to have a reperatoire of techniques to mix and match. Give it a try and see how it works out for you. But you don't have to be married to it.