This is written as Harry Potter's own textbook for Hogwarts. Obviously, it's J.K. Rowling writing as a character from Harry's world. It serves more as a reference to readers of the Magical Creatures in the series.
The movie that is coming out by the same name in November of this year (2016) is based on some of the creatures referenced in this book. I do believe the main character in the movie is actually the "author" of this book, Newt Scamander... And, I cannot begin to describe how excited I am after watching the trailer. The movie is basically the reason I read the book. view here
It's a super fast read. As in, it took less than an hour and half. It's a cute little fun companion to the series. It reads like a encyclopedia so it's not super exciting but it's nice to try and remember all the magical creatures from the Harry Potter books. I think it's profits goes to charity of some kind.
It also made me want to re-read the series which I plan to begin very soon!