Rick,
The MTH web site does not show the WiFi book in stock. Will they be getting more or is it under revision?
There are two different books. Both are always in stock. eBook versions are downloaded from MTH's Kibo/Shopatron website and softcover books are fulfilled by Amazon.
The DCS Companion 3rd Edition discusses DCS from the perspective of the DCS Remote, and only briefly discusses the partially-featured Standard version of the DCS App. It is available here.
The DCS WiFi Companion 2nd Edition discusses DCS from the perspective of the full-featured Premium version of the DCS App, and only does not discuss the DCS Remote operation at all. It is available here.
Each of the 4 web pages, eBook and softcover book, has a "Buy"link mid-way down its page.