I read Jim Johnson's book because it's been getting a lot of buzz around forums that are concerned with such things. It's only around 100 pages and then an appendix with various docs that may or may not be amusing (birth certificates etc). Basically, it's concerned with the case of Ollie Roberts, who was a claimant to Billy the Kid (and the basis of Young Guns II). It hits one (one?) chapter on John Miller who was a much more credible individual, but some of the documents provided here shed a lot more doubt than anything else I've seen. This is good because everyone seems like are side stepping this guy completely.
I've always thought Bill Roberts claim was completely full of shit. It's become even more apparent in the years since his life as we've uncovered a lot more about the life of the historical Billy the Kid. This book basically goes along with what I've always thought on the matter. But unlike most other articles or books about him, it not only transcribes William Morrison's account of Bill Roberts, but it provides a play by play based on contemporary knowledge. It's definitely not for the uninitiated. You need to know a little bit about the history of Billy the Kid in order for this to be an interesting read (You'd be wise to start here if interested).
I was very disappointed on how this book is almost entirely about Brushy Bill Roberts. It's trumped up as a look at all the possibilities of who Billy the Kid really was, theories on alternatives to accepted history of his origins, and that occupies a grand total of 2 out of 8 chapters. I suppose for people who've only seen Young Guns II this is a worthwhile read to see how full of shit the real Brushy Bill was. But for this thing to be making the rounds amongst the more prominent forums is kind of lame.
All in all, I'm not as thrilled with this as I was Wallis's take (although they aren't necessarily from the same angle). I think Johnson has a lot of accounts and accepted history in here down well, and the appendix is interesting because a lot of the documents can't be found online (if you're into that sort of thing). But it's here if you're so inclined.