This book has a less than stellar reputation. I did find it a great way to break the ice as I began studying for the GMAT. Anyone who is planning to use it alone should do so at their own risk as it has not been updated recently and doesn't help with difficult concepts and questions. I did, however, find the techniques and concepts easy to remember because of the book's witty presentation style.
I ended up with a 720 and so I do reccommend buying GMAT for dummies but also take a look at PR or Kaplan
and of course, the OG.