When I first heard about these O'Connor fiddle books I was actually pretty excited. I am very open to the idea of teaching kids pedagogically using American tunes and the fiddling world has been long overdue for something like this. This is a genre of music that really needs to be systemized. As in, there needs to be readily accessible books/tools for teachers to use with their beginning students.
So in that sense, this book does a credible job. It nicely lays out fiddle tunes in a progressively more difficult order. The CD accompanying the book is well put together. Throughout the book there are also suggestions on little variations you could add here and there to each piece if you wanted to get experimental and try some improvisation. I actually kind of wish this had been emphasized more since improvisation is such a large part of fiddling.
From a teaching perspective, the O'Connor method book does not teach basic violin technique quite as smoothly as the Suzuki books. I actually wouldn't even point this out except for the fact that there is a forward at the beginning of the book explaining that it's designed with teaching violin technique in mind.
Each Suzuki piece builds on itself by adding one new technique. For example, once the student learns the Twinkle variations and Twinkle theme, Lightly Row adds using the individual second finger. Every other skill required to play Lightly Row aside from the individual second finger is the same as Twinkle Theme.
The O'Connor method starts off with three Boil Em' Cabbage Down variations. Basically, three of the Twinkle variations. The next piece in the books is called Beautiful Skies. In order to play this piece, the student must be able to string cross while changing bow directions (something not covered in his Boil Em' Cabbage variations), be able to quickly change bow patterns (long notes vs. short notes), and start figuring out how to use the third finger more efficiently. That's a huge jump in skills required. If you're teaching a young student (4 or 5 years old), that would mean potentially weeks to months of preparation time before the student could even begin to tackle their new piece.
So as a smooth introduction to the fiddling style I would say this book is definitely worth checking out, especially if you're looking for pieces more at the beginner level. As a method book for teaching violin technique, it would be useful if the student was older (8 or 9) but would still probably require some supplementary material to fill in the gaps.