I purchased this book because I had already been interested in reading the author's Houses that Change the World. So when Barna came out with "The House Church Book," I bought that one instead, since the description reads, "Houses that Change the World (originally published in the UK) is... Now revised as The House Church Book." After I finished reading The House Church Book, I came to the "Recommended Reading" page, only to find listed, "Houses That Change the World -- If you wish to study the subject of house churches further, Houses That Change the World is the 'big brother' of the book you have just read."
I am now reading through Houses That Change the World, and what it appears Barna has done with The House Church Book is to simply make an abridged version of Houses That Change the World, polish the editing, and update some of the facts, figures and "dated" comments. In essence, The House Church Book is just a "leaner" version of Houses That Change the World. I think it is misleading to call it a revision. The content of the new book is virtually identical to that of the former, it just contains less of it. One might argue that Barna edited out some of the "unnecessary bulk," and it would certainly be a less threatening book for someone who is just getting their feet wet with the idea of house churches (it's under 175 pages, versus over 300 for the previous book), but, personally, I prefer the former book, so far (despite the occasional grammatical and editorial issues).
I would recommend this book if you wanted to give it to someone else to introduce them to the topic of house churches, or if you want the most up-to-date facts and figures (though there are not enough of them, in my opinion, to make this a determining facor). Otherwise, I would go with Houses that Change the World for Mr. Simpson's full picture of house church (and to save a few dollars).