I felt The Hiram Key to be a very good work considering the amateur nature of the writers when it came to historical research and writing. Most with historical training would never have made the leaps of faith they did in some of their suppositions. One of the first things you're taught when working on a history degree are the differences between logical reasoning and logical fallacy, which their theories (at least in THK) were rife with. You also learn that one historical source is not enough to prove veracity, but that's somewhat ameliorated by the thought that perhaps the ideas were so "secret" that they only appeared in a single historical source (also the oral-aural manner of Masonic teaching works against researchers here as we'll).
I have not read their further works, although I've heard the Second Messiah is very good as well. I'll probably look into picking it up in the near future, particularly if I can find it set up for the Nook.
TU
Sent from my iPad while I'm rocking' with Tapatalk.