This book is purportedly a "real" translation of the fictional book made up by H.P. Lovecraft. During his lifetime, Lovecraft repeatedly made references and even explicitly stated that the book was fictional.
With that in mind, Simon's Necronomicon, as it is known, should be viewed as a work of fiction - despite what the authors say otherwise.The book begins with a lengthy introduction about the context of the "translation" as you may expect for an important text like The Inferno of Dante, for example. The book then launches into the "Mad Arab's" writings.
If the whole thing is non-fiction then it is a shame that for some reason the authors decided to translate the text in broken 16th century English. There are also no explanatory notes anywhere in the book for the reader to follow or understand the plethora of unusual names, and places. This is a shame as it ends up being a difficult read when you have no context to about 1/3 of the content.
If this book is a work of fiction (pro tip: it is) then the publisher and author should be ashamed at the quality of the story and writing. There are far too many childish and ridiculous spells or repetitions of phrases as if to make it seem authentic. The chants and incantations are ridiculous and don't seem to relate to one another or have any real point - very few of them seem to be aimed at doing anything in particular.
Interestingly for a book that is marketed based on its occult affiliation, most of the book is devoted to the worship or invocation of the "good" Gods and spirits with only one very disjointed chapter ever referring to anything vaguely sinister or demonic.
It is worth noting the historical context of this book. During the 1970's, largely in America, there was a lot of sensationalist media coverage of the occult or paranormal. In fact the Necronomicon was released in the same year as the infamous Amityville Horror.
Overall I was hugely disappointed by this book. I was intrigued it's cult status but came away feeling as though I had been duped into reading a poorly written children's horror book. More Goosebumps than Lovecraft.