I have taken both Quant and verbal test from GMAT club. Verbal test are good to practice for the timing. Verbal test are good to brush up the basics. I would not suggest you study concepts from these tests.
Quants test are really good best i have seen till now. Difficulty level of these tests is above what GMAT would give you on the test day. If you are scoring in the range of Q47-Q49 on these tests then you are good to go. These test cover every concept which GMAT can ask you on the test day. There are some question which will make you depressed as they would be very tough but don't loose hope as you will learn some valuable tips and tricks from these tests. These tests will time you for the test day.

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