Personally, I haven’t bought the book because of this. With all the options out there it gets confusing for new people to come on board and I think they tend to stick with what MDG puts out. ie. the guides, tutorials, etc…
By the way there are no paid meteor books produced by the authors of mantra or officially sponsored by MDG. So perhaps you are referring to discover meteor, but that book is not officially affiliated with the developers of meteor.
I personally found Mantra to be too abstract. As a developer, I like knowing what’s going on in my app and to properly use mantra, one needs to dig into it quite deep and it is not a fairly easy task. What I found out for myself, when I did that, is Mantra is not designed for Meteor. It looks a lot like a carefully and intelligently designed escape hatch where one can easily switch out Meteor for another backend.
I also believe the wording with “it is for production scale mid/engerprise apps” to be very very very misleading.
Given that all developers on a team are very familiar with how Mantra works behind the scenes, it can be a very valuable “discipline” for getting multiple people to work on the same UI codebase. But that’s not mutually exclusive!