I have used GMAT club tests for my preparation for the exam, and I am thoroughly pleased with the quality of the tests. The maths tests in general help one prep really well for the actual examination. You get more than 20 tests to practice from, sufficient to develop one from Q45 to Q50. Moreover, the solutions presented are crystal clear.
Additionally, the dashboard helps to track your scores, and also the strong and weak areas. Looking at the weak areas, I could improve my quant score by focusing more on Statistics, and probability.
I would highly recommend people to use the GMAT club tests.