The safety squat bar is great for volume training (multiple reps and sets) because of the lack of strain on the elbow and shoulders during the movement.

Pausing on the box for even just a second is extremely beneficial, it teaches you to fire up from the bottom of the squat. Make sure to keep the chest up and think about leg pressing the floor, not squatting.

The back should have little to no movement in it during the squat.