Keep in mind that the textbook you use to assist your studies is not the sole determinant of your performance in the HSC. To do well in the HSC, you need to have extensive knowledge of the course content and proficient skills in applying your knowledge to solve practical problems. On top of these, you also need intensive, targeted exam training.
It is true that MIF's explanations and questions are unimpressively simple, but this makes the book a good resource for self-learning as a stepping stone to developing a thorough understanding of mathematical concepts. Cambridge is a personal favourite because its rigorous explanations and exercises enable the development of extensive knowledge and proficient skills in maths. People who find Cambridge too chunky to chew should consider using MIF, or another textbook, to help them gain a basic overview before tackling Cambridge.
Without doubt, it is beneficial to access as wide a pool of resources as possible. Exposure to a variety of questions allows you to become more flexible in the application of your theoretical knowledge in any situation that may arise.
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Edit
@kony: It just came to mind that you never actually bothered to read any of Pender's explanations. I'm yet more impressed.