I am taking a "Twister" class tomorrow at my LQS. The book is optional to purchase, but it's $18.00. Do you think it's necessary or worthwhile to get the book?

If it is Bargello I would say that is a definite YES.

I bought the small ruler and the book, wish i had not spent the money for it. It is a nice book, has quite a few patterns, but i would wait and see what you learn in class before buying it.

I bought the ruler alone and it has directions on using it.
Not sure if I'd want the book until you see how you like the class, just MO! I don't really care if I have the book or not.
I'm getting tired of buying books with all the great stuff here and online.