I took the exam recently and did not pass.
I did learn by doing the Fundamentals and Onramp Courses twice, as well as doing the "Programming Techniques" and "Visualization" courses. Furthermore, I created Screenshots all the way into all courses and examined the PDFs seperately. I also used them to create mindmaps in order to gain a comprehensive view of all different data types and their uses.
I found that the exam did not have much to do with the Fundamentals course. I saw people writing, that the problems were literally the same as in the Fundamentals course and this is not true. ZERO questions from the Fundamentals course were in my test. There were some problems, which could be solved by using knowledge obtained from the Fundamentals course, but in my estimate, it could only carry you through ~30 % of the test. The test included commands, which were not introduced in the Fundamentals course and weird special cases of using "surf" for example (very weird vector compositions, not at all how it was introduced). You will also only get a "failed" notification and no feedback at all. So you don't even have an idea of how to improve.
I started CODY today and it is fun and will certainly teach you well, but it doesn't adress anything in the direction of questions from the MATLAB test, so I will not continue with it for preparation. I will certainly do the test again and I am determined to pass this time around. My recommendation: do not underestimate it and really try to apply the MATLAB commands on very weird cases/ "test the limits" of the commands