I just got a copy of the Alexander and Elias-Bursać textbook. I will say that it looks like it's intended for classroom use, so it's going to be a bit rough for self-study. For example, the pronunciation guide includes no explanation of phonemes that do not occur in English, e.g. hints on how to distinguish č and ć. The FSI textbook is much more thorough there. The grammar explanations are also a bit light for my taste--I'll take excessively thorough explanations that use specialized terminology over "simple" and "easy" explanations any day--so perhaps I should have gotten the grammar book as well.
The main appeal of this book is the way it presents all three languages together, along with occasional commentary on Montenegrin. Having every dialogue written out in all three languages is interesting and helpful. That said, a total beginner like me has to pick one to focus on at first, so I'm not really able to get a lot out of that aspect of this textbook.