The main two books I read when studying the Maya script were this one and Michael Coe's "Reading the Maya Glyphs." Ultimately, I preferred this one because it is more in-depth and scholarly, but I did miss the exercises and easy-to-look-up tables that the Coe has. The Coe is also slightly better illustrated (or, at least, more flashily illustrated, which is admittedly not the same thing). Either book can add greatly to your appreciation of monuments at sites such as Palenque and their museums, and ideally I would recommend purchasing both books.
I'm somewhat conflicted about this next issue. The Coe book delves further into some more cutting-edge grammatical theories such as morphosyllables and syllabic disharmony (don't worry, both are explained well). These theories are fascinating, and are barely discussed by Montgomery in the book on this page. HOWEVER, there is far less scholarly support behind these controversial ideas, and in many ways I think Coe makes them seem more accepted than they are. Montgomery's conservatism is probably more academically honest.
It's very difficult to recommend one over the other because they both have their strengths and weaknesses. It may be overly general, but if you're looking for a more sophisticated and deep understanding of Maya script, the book on this page is probably better. If you want a more practical study (including exercises to test your comprehension), go with the Coe--just remember that scholars are less certain about some of his claims than it may seem.