I don’t like them. Not only are they too draining to be much of an assistance exercise, but I don’t like the stance they force you to take.
The wide stance and externally rotated feet the exercise requires can teach bad activation patterns and can cause one to walk, run, or jump with externally rotated femurs.
Funny, they don’t force me to take a different from the usual stance. Also, they are an alternative for the full squat in the fall and winter, not an assistance exercise. In the season, together with Olympic lifts, box squats are the staple of my lifting, just higher than in the previous months.