Hi GreginChicago,
GMAT Ultimate Grammar is a very detailed grammar book. If you really want to understand in depth grammar concepts please put this book in your study plan.
During my preparation times, I really couldn't manage to pull out much time, so I never got to really absorb this book. However, whenever I was stuck while reading
MGMAT SC book and needed some conceptual clarification, I referred this book.
However, I didn't like the practice questions within this book. They didn't seem to be too relevant to the GMAT present SC level.
I would advice you to go through the free version of this guide, see how it suits you, and then go ahead and buy it if you like it.
Hope it helps.