Donald Maas's workbook is an extension of his book WRITING THE BREAKOUT NOVEL. For me, the workbook format helps me put his techniques into action. I would suggest using this book for initial brainstorming of plot and character formation, although he often writes as if a complete draft is before you. He relies heavily on reversing ideas (i.e., if you have an idea, take the opposite idea instead), which tends to get you out of the rut of going with your first idea or a superficial idea.
As I've mentioned, he has several exercises for developing plot without being linear, which to me, is a nice departure from scene cards and the three-act structure. However, it's a challenge to put the ideas then into sequential order. My only gripe is that I went back and read the books he suggests as "breakout novels," and I didn't like any of the books he had used as examples. I'm partial to mysteries and that perhaps explains why I didn't like the more literary novels or the romances.