When reading books like these where the author is merely acting as an editor to supply the stories, I try not to judge it on the storys' validities. It's pretty standard that you'll get a mix: some that are genuinely interesting and others that are just off the wall crazy. Reading the crazy is at least entertaining so it has a point of being in the book.
The problems that I do have with this book are more along the lines of (a) how the stories were edited and (b) how some stories really didn't fit the topic matter.
Honestly much of this book felt much like Redfern just literally copied and pasted emails, character for character, from responses he received from prior books on MIB. That shows in several ways. First, the tone of each story is varying; some speak as though they are talking to Redfern, some speak about Redfern with mentions to the book, and some read as if they're articles that Redfern snagged from the web and pasted in. Any one of these is ok, but not all at once. Second, the various grammatical and punctuation errors. I don't understand how not only Redfern missed them, but the author of the article (hopefully) would have looked at several drafts. Lastly, the things that just shouldn't be in a book like emoticons and sentences ending in multiple explanation points!!!!!! :) Is this a book or am I holding a printout of an AIM log?
On top of that, saying that each chapter in the book is "about" MIB is generous at best. Again, the problem varies in form from chapter to chapter: sometimes MIB are only mentioned once as an example or a specific case of a larger topic; sometimes the encounter isn't really MIB but kind of vaguely related ("some guy called me on the phone and threatened me"/"one guy stared at me in the bar then left" - both of which, albeit with hyperbole, are actual stories in the book); or sometimes the chapter will be about an entirely different phenomena like BEK or shadow people or demons and then just say how maybe MIB is the same thing.
There are some awesome stories in here to be sure, and I actually really liked some of the comparisons given like to BEK and vampires, but beyond those small parts this book just seemed like a mess. The tone shifted from casual retelling to academic paper to newspaper article to email messages, and there were way too few stories actually about the MIB to satisfy my curiosity.
I actually got this book at a conference where Redfern spoke and he did an amazing job, so I can only hope the problems came from him being an editor instead of author (at least I hope; this is the first book by Redfern I've read). There were some good parts to be sure and so those alone may make this book worth it for some readers out there but I suppose after getting hyped from seeing Nick give a stellar talk on MIB, the book was a bit of a letdown for me.