In my opinion, now that we have the free "second shot", the practice tests are not worth the money. Just read the "Skills Measured" list in the exam description page to verify that you are knowledgeable about all the topics, and then go and take the
exam. In the unlikey event that you fail to pass, go back and study those topics where you were not sure about the answers you gave, and then retake the exam for free (make sure that you sign up for the second shot when you buy your
first exam).