To stay on topic, my assumption is that this is probably a desk reference, that would be most useful for either studying BEFORE going in the field, or trying to resolve the identity of "odd" flycatchers which may be vagrants. I don't think it's really something written with the assumption that the average birder would be lugging around.
To venture off on a tangent, I am sure many of us have a preference for physical guides. I find digital guides to be most useful when I already know the local bird fauna, in which I only use a guide in the rare case of me seeing something unusual or a difficult plumage. I have the Sibley app and I can't be the only one who finds it a lot less useful than a physical book, as to find the bird in question I need to physically type in a name, which means I need to automatically have it narrowed down to a degree. Versus a physical guide, where I can go to he relevant section and flip through in a fraction of the time, and direct comparisons between species are easier. I can't imagine being able to use a digital guide for a trip to a location with bird faunas that are completely alien to me (old world, neotropics, etc), even with advance study.