I have updated the Wikipedia page on the FASP protocol they compete with, to provide more detail on how it works. Theirs might work similarly.
Curiously, FASP usage only really took off after the product got a comprehensive GUI file management app, with scheduling and a speed control you could drag up and down. Being able to transfer files overseas several times as fast as the competition was not enough.
FASP was on HN a couple of years ago, https://news.ycombinator.com/item?id=21898072