So, I'm not terribly knowledgeable on the subject, so please excuse and correct me if I am completely off base here...
Okay, so, as I understand it, a lot of people think that after the war he fooled everyone into believing he wasn’t that bad of a guy. In reading about this, I stumbled on a book by Matthias Schmidt claiming to point it all out, 'Albert Speer: The End of a Myth.'
Well, I was looking at it on Amazon, and in the summary there was an entry praising the book by a Mr. David Irving.
David Irving seemed like a familiar name, so I looked him up and apparently he’s a Holocaust denier…?
So what the fuck is he doing praising this book, a book that professes to expose Speer's hand in the Holocaust? Do I have the wrong David Irving? Do I have the wrong idea of the book?
Since your question's been up for almost a whole day without any real answers, I'll give it a go.
I believe that you probably have the correct David Irving. Irving has been around for a while, and his views (or at least his willingness to be public about his views and put them in print) have evidently changed over time, from simply questioning in the 1960s-70s the 'official' story of the Holocaust on various points, to outright denial and neo-Nazism in the 80s-90s.
At the time the book you link was published (1986), Irving wasn't yet publicly denying the Holocaust, and although his various works had already been dismissed by fellow historians as being inaccurate and revisionist, those works were nevertheless popular with the public (e.g., Hitler's War, The War Path, etc.) and he was (and is) fairly well-known for a 'historian'. Also, not too long before your book here was published, Irving was famously involved in helping to prove the 'Hitler diaries' were fakes, which only increased his visibility.
So, in 1985-86, Irving was certainly famous enough to be sought out for back-cover blurbs to help sell books, and not yet too whacko/controversial to entirely scare away mainstream publishers (e.g., "Hey, we have this book about the Holocaust to sell, let's get that controversial guy who also writes popular Holocaust books to praise it...")
As for why Irving, as a denier, would want to praise this book--again, he was evidently not a full denier yet, so it's not necessarily inconsistent with his views at the time.
From wiki's article on Irving, which pretty thoroughly details his career:
Over the years, Irving's stance on the Holocaust changed significantly. From 1988, he started to espouse Holocaust denial openly; he had previously not denied the Holocaust outright and for this reason, many Holocaust deniers were ambivalent about him. They admired Irving for the pro-Nazi slant in his work and the fact that he possessed a degree of mainstream credibility that they lacked, but were annoyed that he did not openly deny the Holocaust.