Design and Form is a solid text, with many examples of the type of work that Itten tasked his students with. Itten does not, however, lay out a series of lectures for the student. Rather, Itten lays out a path of experimentation and self-discovery for the student to follow. Much of the content will be familiar to anyone who has read The Art of Color, and for those people, I could not recommend buying (nor could I recommend avoiding) this book. If the reader needs clarity on a subject, many examples prod the reader into finding a solution.
In sum: A good (but not great) text when considered on its own merits, and an average text when considered in conjunction with Itten's other works.