I've been using the Starter Series DD for over a year. Very good physically, big movement, and cognition. It would be an improvement for me (and probably others, if Nate did not use letters B. C. D. E for hand and leg movements in some of the exercises. It's too hard / impossible to tell which one he's said, and while I'm fumbling around I get behind and use coordination. So please use letters that sound different A. B, F, H, etc., or numbers or names that don't rhyme.