I'm doing the lessons.
Fair to say that the first few etudes are really quite easy. But also that the last ones (In the Beginner / Intermediate pack) are quite difficult. For me anyway.
Comparing to my daughter's clarinet studies I would say the early ones easier than Grade 1 Trinity, at Lesson 24 (the last lesson in this pack) are about a Grade 5 level.
The first pack really is aimed at learning to read music - every exercise is in C.
Pack 2 introduces the sharps and flats and Pack 3 is Scales. Pack 4 is Chord Tones.
It's quite odd with everything being in C, but my experience of reading is from Sax and so with that just about nothing is in C!
I'm going to try and do 10 or 15 minutes per day just reading as recommended by my daughter's amazing clarinet teacher.