I am not familiar with the instructor, the book nor the technique so not sure how much my input will help. IMHO It totally depends on what is involved with the technique. For example with paper piecing I had looked at written instructions on how to do it and couldn't grasp it but I took a class and totally understood. The class included handouts but it was the hands on that gave me my "aha" moment.
On the flip side of that coin, I have self taught myself using books countless other quilting techinques such as freezer paper piecing, needle turn applique, set in seams, strip piecing. I tend to like to have a book to refer back to. I may not remember what I learned in a class if I don't reuse the technique for several years. I think only you can answer this question because you are the one who knows how you learn best.
If you take the class and practice the technique enough afterwards that it is committed to memory then take the class. But if you don't think you will use it again soon then you will need something to help refresh your memory. Have you thumbed through the book? Is this something that will interest you for many quilts to come? If not I wouldn't take the class nor buy the book but use the limited funds on something that you will use a lot or fabric
