Box Front Squat is an excellent exercise that helps to develop muscle feeling and balance for correct mechanics of the Front Squat.
From my coaching experience a lot of athletes have troubles with the correct start of the movement. Often, they initiate the squat by moving knees forward instead of hips backwards. The box front squat exercise will help to fix this problem.
Please, keep in mind that this drill doesn't 100% simulate body behavior with heavy loads, but will help to build the correct feeling of body parts and muscles. During normal training with the front squat your knees will pass over the toes which is totally fine.
Remember that Box Front Squat is a training exercise for the squat movement. Not the actual movement of how the knees will move.
I recommend doing this exercise as a #WarmUp before #Clean & #FrontSquats - 2 - 4 sets, 6 - 8 reps each.