The Gmat club tests are easy to use, there are easy explanations. The quantitative questions are great and the explanations are easy to understand. The best feature is the ability to select questions of varying difficulty. This way one can gradually challenge ones self. Verbal questions - Some are not indicative of the actual type of questions one would get in a test but they still good practice. I would highly recommend these for anyone who wants to focus their efforts on high quality questions.
1)Topics are broken down into subtopics
2) Quiz tool is very very beneficial, you can set up your own quizzes from Quantitative or Verbal. Verbal Quizzes can ahead be subdivided into SC, CR or RC or you can mix all questions up. And the difficulty level of these questions is very high.
3) Highly detailed CAT's, this is pretty self-explanatory.