I agree with Flipp. "One size fits all" is not the way to approach it.
We "bit the Mills bullet" a few years ago, more out of curiousity that anything else. And, long-story-short, our package now sits in my attic. However, I will say that there were a few things that we found helpful or useful. He does do a fairly good job of explaining the importance of balance, and has a few pretty good drills that help. Also, one of the videos was on how to read hitters. However, we actually used this video for our catchers to teach them the basics of reading hitters, and not our pitchers. IMO, I found it all to be kind of a "pitcher in a box" system, which did not allow much individuality in the delivery. I think it works well for beginners, because of it's effectiveness in explaining basic balance techniques. In our case, we found it to be something that you implement a few ideas, rather than rely on solely. I also found it to be very "timing critical". If all timing aspects of the upper body, lower body, hand break,etc. are not perfect, I think it lends itself to potential injury.
In the end, I don't think that you would learn anything different that any semi-knowlegable instructor would be able to teach...and at a much lower cost.