I have used these in various training over the years. I found that myself and others have used a box about knee height. Which seems to be the general rule of thumb (or knee). But that would be personal choice, of course. The hams are also worked extra hard, as are the glutes.
Have also used the extreme height as in the picture for short periods. In any event a very productive movement for most sports and athletic training. Even the weekend sports warrior. Great for balance and working one leg at a time can give a better feel to the exercise. And can improve BB squats with better balance
The free leg and placement that is on the floor can be also important, which determine the important stretch to the movement. Some may find that a extreme box height of the box shown in the picture will not be needed, depending on the distance that the foot takes backwards (close to far). Might also suggest DB's when starting off with this movement. Tend to be a question of balance if new to this exercise. Usually high reps like 12 to 15 for general training. Sets are up to the individual, as always.
Good Luck