It is very unlikely that you will need or ever use the Calculus 1 textbook, but given the higher complexity of the course problems and more mathematically-focused teaching when compared to VCE Specialist Maths, doing problems from a VCE Spesh book will only help so much (the exam for Calculus 1 is very difficult without a large amount of preparation, despite quite simple concepts). If you are good at keeping on top of study consistently and have time at the end of semester after doing literally everything else you can do for the course problem-wise, the prescribed subject textbook would come in handy. However, it is more likely that it will be of no use to you for things other than extra problems (which are good to have in this subject; in 2013 the exam questions were -mainly- harder than the assignments, tutorial sheets, lecture questions and problem book questions). Either way, for the price, this book isn't worth buying, but if you can get your hands on a discounted copy and feel like you'll find time to use it I would definitely suggest it.