GMAT Club tests really helped me build stamina and exposed me to a wide variety of questions.
However, I would recommend using them only after you have completed all the topics and want to focus on improving your test-taking stamina, sitting endurance, and time management.
The Advanced Tests are particularly useful because they use a scoring algorithm that closely mirrors the actual GMAT, providing a fairly accurate estimate of your performance and detailed analysis.
Another feature I found helpful is the option to attempt individual sections separately. This is great if you want to focus on improving a specific section without having to take a full-length test.
Overall, these tests played a significant role in helping me complete the actual exam on time and better understand my strengths and weaknesses.