The exam is a little bit difficult without participating to an official course. But it is not impossible. I have received emails from people that have passed the Spring 5 certification exam by working with my previous book(which was writen for Spring 4) and filling up the gaps using the official Spring Documentation reference.
I can confidently assume at this point the 2nd edition of the book, written for Spring 5 will be even more helpful.
Nonetheless Spring changes fast these days, so as long as you keep your eyes on the official Spring blog and the official Spring certification page and go throught the official study guide throughly, you should be fine.