Hi, Suzy.
Did you know you can look these and any other books up on Amazon and usually find reviews by a range of readers (which in my experience often give useful pointers as to content, coverage, useability, etc)? For example:
Year Round Messier Marathon Field Guide
Prices (especially used), are usually better than local sources too, even with postage added.
Incidentally, as the Messier objects were named by a wholly Northern Hemisphere astronomer, there will certainly be some that are restricted/impossible from Australia. You're quite northerly where you are though, so you'll do better than those of us who live further South!