I passed the Essentials and 220-602 tests using only A+ Certification All-in-One Exam Guide, Sixth Edition (A+ Certification All in One Exam) and this book. In addition to the practice tests in this Cliffs book, I used the practice tests in the CD that comes with Meyers' book, and additional practice tests that come bundled with CompTIA test vouchers purchased from Meyers' company.
The Meyers' tests were easier than the tests in this book. I passed the Meyers' tests with scores over ninety percent. Then I took the practice tests in the Cliffs books and got about forty percent of the questions wrong. This was true for both the Essentials and 602 tests.
I found that the degree of difficulty on the actual test is closer to the Meyers' practice tests than the tests in this Cliffs book. My performance on the Cliffs tests unnecessarily made me question whether I was adequately prepared for the actual certification tests. However, I learned valuable information from the review of the correct answers in the Cliffs book that will be useful in the real world.
Taking many practice tests, noting my errors, re-reading the relevant sections of the Meyers' book or looking up the information on whatis.com, and re-taking the practice tests was a successful strategy for me. If you want to follow that strategy, go ahead and use this book. If you do well on these tests, you should feel confident about the actual exams!