I strongly recommend

Gmat Club Tests are very helpful especially when one aims at 700+ score. Tests are composed to enrich one's skills in hardest questions. Real GMAT is a little bit easier. But practicing harder questions will help you be more successful in real GMAT. On the other hand, GMAT Club tests are more focused on Quant section, so verbal section is much weaker and I used another courses and sources to master Verbal. I really appreciate the option to train only specific topic of questions with specific level. This has helped me a lot in practicing weaker parts of my GMAT test and surely helped me to score more in real test. To sum up, if you want to brush up your quant, I fully recommend GMAT Club Tests. On the other hand, if you feel weak in verbal, you should try to find any other course as a core one and use GMAT Club as a subsidiary source of materials.