I've read my fair share of iPhone "manuals" and how to books since picking up my iPhone 5 a month ago. Before I started I considered myself to be iPhone proficient, but realize now that I'd barely scratched the surface of the device. I'm getting now to the point that I'm not picking up a ton of new information with each book, but I think that their teaching styles vary enough to warrant reviews and comparisons.
The iPhone 5 for dummies book is the middle ground of all the iPhone 5 how to books. It provides enough information to get you up and running, it does it in a fairly readable fashion without bogging itself down with step-by-step, button-by-button guides (like Teach Yourself VISUALLY iPhone 5 (Teach Yourself VISUALLY (Tech)) can tend to), and it stops itself before getting into secondary information that isn't required for operation (like iPhone: The Missing Manual does).
The book is designed to be read cover to cover, but has a decent index and can certainly be used as a reference. It starts with an introduction section about the book itself and follows with the following sections:
1) Getting to know your iPhone:
This section covers the basic phone design (where the physical buttons, microphones, and cameras are), very basic phone use (on/off, answering a call, typing, syncing your contacts and music etc.). If you've used an iPhone or an iPod touch before this is a section you can skip.
2) The PDA iPhone:
This section covers siri, imessage (test messages), the calendar, the clock etc. Its probably another section that you could skip if you've used an iPhone before, but it does have some helpful tips and hints that are new to iOS 6 and the iPhone 5.
3) The Multimedia iPhone:
From iTunes to shooting still photos and video this section covers what you should know about the built in multimedia apps. This was one of the sections that you probably won't want to skip as a lot has changed in the camera apps including the addition of panoramic shots and new editing options.
4) The Internet iPhone:
If you have any problems with safari, email, or any of the built in Internet connected apps like weather or stocks this is where you'd want to look first.
5) The Undiscovered iPhone:
If I could buy one section of this book individually this would be it. This section hits on the settings you can use to make your iPhone work for you from airplane mode to iCloud to general trouble shooting. This section is well laid out and probably has the most helpful information in the book. I've always thought that while apple does great interfaces for general use, their settings section can be confusing and this section would certainly help.
6) The Part of Tens:
This final section has two main topics. One I love (the hints, tips, and shortcuts section) and one of which feels like fluff (the "Great" apps section). The tips section has some of the best tips in the book outside of section 5. Storing files, making free ringtones, optimizing autocorrect. They're all really good little reads. They probably could have fit into other sections of the book, but at least they've been included somewhere. The apps section seems almost silly. There are 700,000+ apps in the app store. The store itself has a rating system, a featured apps page, and subcategories that list the top games, productivity apps, lifestyle apps, etc. Most of the recommended apps in the book have great ratings, are long time top sellers, or are currently featured. In short, if the section on finding quality apps was good then this section was extra. Its not new its not ground breaking, its might give you an idea of where to start, but picking 20 apps from 700,000 gives such a limited picture of what the app store offers that it seems a little silly to include.
So that's my chapter content run down. I'd rate the content as being fairly comprehensive if sometimes a little thin compared to other guides, but its certainly enough to get you going and enough to let you unlock 90% of your phone's functionality.
I'm a little disappointed they haven't opted for the "look inside" feature because I think the readability of a reference book is nearly as important as the content, but if you want to compare writing styles Barnes&Noble's website has a free "preview" of the book that you can take a look at (it covers just the index, intro, and start of the first chapter).
Overall I thing this is probably one of the strongest guides for someone that wants a readable reference (not lists of button-by-button commands) and doesn't care about the fluff that makes the phone work, but doesn't contribute to their user experience. It's not my favorite guide (I'm a bit of a geek that likes that fluff and this book wasn't written for me), but it has a well-defined target audience and it is exactly what they're looking for.
UPDATE: COMPARATIVE RANKINGS
I never intended to read enough iPhone 5 "manuals" to truly compare them. First I just like learning about the phone. Then I got interested in the differences in teaching styles and ended up reading 5 really well put together books. I ended up rating them all relatively highly simply because they were all great books that will serve their target audiences very well. But since they're all great books you deciding on star ranking alone may not get you the right book so I'm adding a comparative ranking to each of my reviews to help you identify which target audience you might be in.
I still stand by my initial reviews, but with more background my perspective has definitely grown.
1) The Missing Manual (iPhone: The Missing Manual) - Covers from the tech in the phone to multiple ways to do almost everything
2) My iPhone (My iPhone (Covers iPhone 4, 4S and 5 running iOS 6) (6th Edition)) - Maybe a touch less tech coverage than The Missing Manual, but not by much
3) iPhone 5 for Dummies (iPhone 5 For Dummies (For Dummies (Computer/Tech)))- A reasonably comprehensive guide that doesn't bog down in tech detail and covers fewer ways to do things than the missing manual
4) Teach Yourself Visually (Teach Yourself VISUALLY iPhone 5 (Teach Yourself VISUALLY (Tech))) - just a how-to usually one method per function
5*) iPhone 5 for Dummies for Seniors (iPhone 5 For Seniors For Dummies (For Dummies (Computer/Tech))) - A moderately distilled version of the dummies book with more focus on "senior specific" topics
(*I thought this should be singled out for its special topics of interest which my override total comprehensiveness for some buyers)
Readability and Narrative:
1) The Missing Manual - Reads well and the author has a bit of a sense of humor. The lack of walk throughs actually tends to make reading flow more naturally
2) My iPhone - The narrative in this book made it accessible and helped disperse any nervousness you might have about learning a new tech device
2) iPhone 5 for Dummies - A readable book, but certainly not my favorite read and probably not something I'd read for fun (even if I am a bit of a tech geek)
4) iPhone 5 for Dummies for Seniors - Big text make this book "readable," but I wasn't engaged with the narrative
5) Teach Yourself Visually - This book is walk throughs its not for light reading
Walk throughs and step-by-step instructions:
1) Teach Yourself Visually - Tons of brilliantly detailed instructions with pictures that point out exactly where to press
2) My iPhone - Nice guides offset from the narrative in distinctive blue boxes with helpful pictures.
3) iPhone 5 for Dummies for Seniors - More guided instructions than the regular Dummies iPhone book, but not close to the Teach Yourself Visually book that I would recommend to my parents in terms of quantity or quality
4) iPhone 5 for Dummies
5) The Missing Manual - Step by step, button-by-button guides are not emphasized. The book isn't void of all instructions, but they are imbedded in text and assume that you read the first chapters and can find the appropriate buttons.