I first saw these on the evening news. A teacher came up with the concept to help her children who could not keep still. The child put his foot on the bar at the bottom, and literally pumped it back and forth. The movement allowed him to do his work, and kept him from distracting his fellow classmates.
I was astonished to see what appeared to be a class full of working children. Yet "under water" their feet were going a mile a minute! (I immediately wondered when someone would come up with the idea to convert all that energy into running a small refrigerator, or something similar, LOL!)
The desk is adjustable to allow the child to stand or sit. And every year I have students who could benefit from this!