We just started Fractions yesterday and we're already on chapter 6. We love it! We are using it as a supplement with MM, but at the rate we're going he's going to get to the new concepts in LoF before they are taught in MM. I guess that's already happened, though, since he didn't know radius and diameter before yesterday. He's very mathy so I'm not worried.
I'm using it in a similar fashion to Paula. DS9 is an excellent reader but since he wouldn't wait to start the book and I wanted to make sure he was understanding, we're reading it together. Also, I was very interested in seeing what all the excitement was about. :) We cuddle on the sofa and I do most of the reading. He does the math and anything he can do verbally, he does (fine motor issues).
I'm enjoying it so much I plan on purchasing them all. But I can see they wouldn't be for everyone, and in fact, DS13 isn't interested at all. He sat with us when we did the 1st chapter but he'd much rather have a textbook.
Debbie