Mock tests are quite useful in assessing your current state of preparations as well as getting valuable practice of exam mode. However, they are not a substitute for building your aptitude. I have seen several people just take a high number of mock tests and look at the solutions thinking this will help them in the actual test. If you are one of the people doing so, I suggest you stop right now.
So what do you need to do then? Once you take a mock analyze your performance by checking the questions you could not do and also the questions where you took more time than normal. These will decide your corrective actions in terms of dealing with your aptitude gaps. For example if you could not solve a question on Time & Distance, go back to the basics and understand the way to solve it, then practise a few problems of that nature. Over 20 mocks or so, you will be able to address most deficiency areas and this will get you really ready for the tests. Of course, I am assuming that you start taking mocks when you have completed the syllabus completely in the first place.
For the people in my Coaching cum Mentoring program, I have asked them to take the Cracku mocks and the results are encouraging, given the overall tough nature of the tests. I am advising them on the deficiency areas and 4 months is good time to progressively take care of these. My pure mentoring program starts in August and I will finalize the intake in the next 2 weeks. If you are interested send me a PM and I will get back to you.