I started my Gmat club test almost 12 months ago, i read about other quizz bank other there in there market such as Kaplan and MGMT, and Gmat club offers the best quality/price you can get. The questions are very challenging enven the 500-600 range. The 700+ questions are really difficult and i think you would not find a lot of that kind of question in the real GMAT, but they are good to practice and get you to the 700+ in the GMAT. The only think that i did not like about the gmat club test is that the CATs use the same data quiz bank of the quiz, so if you do a lot of quizzes you are lossing cats. I fully recomend the gmat club test and specially if you at aming to the 700+ range, also i recomend to study and have fully understand the theory before attemting the 700+ range question or you can lose your time and practice questions.