The 901 and 902 are separate portions of the same exam, they don't have to be taken at the same time though some people do. You must pass both for an A+ certification.
The Mike Meyers book is not free , I would imagine it is invaluable though as it comes with several built-in practice questions and likely comes with software with even more practice exams (I'm not sure if this is actually the case with the A+ book, but I have his Network+ book and it came with this kind of thing).
The rub is that if you have enough experience to outright get an A+ certification with little studying, you probably have enough experience that a potential employer might not even care about the A+. I skipped over it and went straight for Net+ and Sec+ certs for this very reason.
Honestly if you've got the time to study and you can get a voucher for that cheap, I'd go for it. It's definitely not going to hurt you by any means.
You keep saying "A+ exam" in your post so I hope you are aware that there are actually 2 exams you have to pass to get the A+ and they must both be from the same series. Be sure to look over the exam objectives (listed here by Mike Meyers and Professor Messer. They're fairly easy exams but they're not that easy and they included a few topics I hadn't been exposed to before I started studying for them.