Jim,
I respectfully disagree. It does not 'recommend' a spare air, it goes over the various alternatives for redundant air sources and talks very candidly about the pros and cons of each. Simply because a person chooses one source over another is not a reason to demean it or them. The Von Maier states that he uses/used one, but also candidly states the limitations.
As for being 'dated' - the information is useful - and sure, we talk about many of the things in the book here on the board, but it is quite nice to see all of this information in one place, well presented.
If we can't learn from what people were doing 50 years ago, 40 years ago, 30, 20, 10, etc, then we aren't doing our jobs. This was updated in 2002 (2nd ed) - I found it a good and easy read and certainly up to the task of educating or at least reminding this 'experienced solo diver' of the realities of both diving solo and the 'buddy' system.