here are the things that make me hesitate: (1) very expensive (even though i'd save money by skipping the classes and just following the book); (2) wastes a lot of fabric; (3) the technique leaves you with bias seams all the way around the blocks. i suppose you could avoid that by cutting strips on the bias to begin with so that you come back to straight edges, but that's just more fabric in the scrap bag; and (4) what if i forked out all that dough and found i didn't like it?
if, on the other hand, a person likes collecting scraps and using them in follow-on quilts the waste isn't really waste. it's just pre-cutting for future projects. and she did have a blast in class, which has a value that's hard to calculate. if you follow the lessons through the whole book, you'll make a variety of quilts after just one time through. and you'll have a versatile tool you can use for years to come.
whether or not it's "too expensive" depends on how much fun you have using it, how many quilts you think you'll make using it in the future, how much time and stress it will save you if you don't want to use traditional methods to make those types of blocks, and - of course - whether or not you can afford to divert that much money from your fabric budget.
a friend of mine has the ruler and the book. she also took a class that required more than one session over a period of weeks. by the time you add up all those costs, it's a very expensive tool. i'm not terribly interested in it for myself, but my friend loves using it and swears up and down it was worth every penny.