The key to this drill is to understand that the setup and the impact are not the same. The longer you can maintain the impact alignments through the ball, the more consistent your strikes will be.
Devan Bonebrake says that when you set up to the golf ball, you should have a fully rotated body near close to the forward knee. The big keys here are a right wrist bent back, a left arm straight, and a left wrist flat. The number one issue that Bonebrake sees when people try to hit their iron shots is called left wrist breakdown. This moves the point of contact with the ground behind the golf ball, raising the launch angle and costing you some distance and adding too much spin.
To practice this drill, set up, make a little half swing more like a three-quarter type shot, swing back, come through and then hold a follow through. The goal is to assess where you are coming through. If your arm is bent like a chicken wing, you can reassess and utilize this drill.