I have used another book from this series, Algebra 1, and I felt that it was great at explaining everything. Maybe it was partly because of my having a wonderful teacher, however I felt that it did a wonderful job of explaining things.
In response to that of the teacher in Illinois, I would just like to say that maybe the 6th graders didn't understand it because Algebra 2 is a high school course, normally taught in that of 11th grade according to the New York State Curriculum. I feel that her comment on the book should be considered invalid, just because of her lack of explanation, and of the time that she is teaching it. I also feel that if Illinois is teaching Algebra 2 in 6th grade, that they had better change their curriculum, because not even the most advanced 6th graders can take in a good understanding and comprehension of the complex subject at that early level.
Please rethink your decision, because from what Illinois is doing, we can find that it probably has a terrible Mathematic curriculum, and that if it doesn't do something soon, they will have many kids failing in the future. I fully recommend this book as it covers all topics neccessary, and has the ability to explain the complexity of the topics to not only a student being taught by a teacher, but also a student reading the book in order to catch up on work.