I have to say, I strongly recommend this book, not only for designers focusing on multimodal, cross-device experiences.
From the philosophical point of view, it's great for any designer, as Cheryl explains that you are most probably already designing multimodal experiences, even if you're not aware of it yet. She has great arguments why and how you should become aware of it, and make sure your already multimodal design is really inclusive. This topic of inclusivity runs throughout the whole book alongside other ethical questions. If you're reading the first chapter and you're wondering whether it gets to anything practical beyond the ethical questions—it will, note the book is longer compared to other Rosenfeld Media books.
From the practical point of view, the book describes how to design multimodal experiences in great detail, providing particular tools, and showing examples for the transitions between modes and devices, as well as for individual modes from sound to haptic and kinetic experiences. If you don't find an advice for the situation you're trying to solve, you'll definitely find what to think about, and where to find other sources. The only disadvantage of these very specific examples and advice is that they will become obsolete sooner or later. Nevertheless, you'll find the book to be useful not only when you're focusing on multimodal experiences, but also working with any kind of notifications, designing sound interfaces, or multichannel experiences.