I like the Krieger videos (Essence and Advanced Essence), and I would recommend them. However if you are an intermediate caster, an hour with an instructor will be of greater value, and the videos and the instructor will be the greatest value. Watch the videos and practice, and work with an instructor to maximize your improvement.
I did not have a casting lesson until I began fishing salt water. I could cast as far as I needed for trout, but now I can cast as far as I need with much less effort and false casting. In salt water with my medium action 9 weight, I was casting about 60 feet before the lesson. After the lesson, I was hitting 90 feet with less effort.