I have used several GMAT books to fully prepare for my big day. The book that accompanies this package is unremarkable. However, I was amazed at the tech quality of the CD ROM: the "virtual instructors" provide the basic facts about the GMAT and its components. The CD is really what you're paying for.
The astute GMAT student will take and review all 4 practice tests on the CD. Please note--the Math sections are A LOT tougher than those appearing on real GMAT. Don't be discouraged by poor results on these sections!
The Verbal sections are over-simplified. I think they give prospective test-takers a false sense of security on test day. Obtain an English grammar/usage book to supplement the Kaplan materials.
Of course, you MUST purchase the Offical GMAT prep-book. ("Ain't nuthin like the real thing bay-bay.") Do the real questions after you've completed the Kaplan tests. You should be peaking at this point. Take the plunge!
Finally, I found it helpful to "log" my errors for each section. That's right, a log. Try it--it works.
Bonne chance! (relax, no french on the gmat)