Well Amrita I didn't follow any of the paid mock exams. I just read the Khalid Mughal book along with the K&B book and then did the K&B Master Exam, Inquisition,
Examlab, and a list of other free mock exams available on the internet. The main recipe behind success in SCJP is being conceptually clear. If you know how GC works, then the questions will look like a piece of cake. And with a lot of practice, the questions on the exam will not be able to confuse you. The questions available on most of the mock exams are tougher than the real SCJP exam, so if you get a decent score on the mock exams, then you'll definitely succeed on the real exam