Mike,
What about the video they sale?
The OGR video is very nicely done, however, it deals with DCS 3.1 which was current in 2009, making the video 6-1/2 years out of date. A great deal of DCS has changed and been enhanced with new features and functions since that time.
The book is current with all of the features and functions of DCS 5.0 and is richly illustrated. The print version and the eBook are identical in content and the 3rd edition contains a section on the DCS WiFi App and the WiFi Interface Unit (WIU), as well as an Index.
Everything that you need to know about DCS is all in MTH’s “The DCS Companion 3rd Edition", available for purchase from many fine OGR advertisers and forum sponsors, or as an eBook or a printed book at MTH's web store!