I have used the primer, first, and now second level books (lessons book and performance only)with just three beginners.
As the teacher, I enjoyed something new for a change, and it seems quite sound.
All three kids are still attracted to their books, and all three are doing exceptionally well, but of course, they also happen to be three very good practicers. (I do supplement quite a bit, so these books comprise less than 50% of their materials.)