We used LoF for most of our math last summer/fall. We started with Apples, even though the first many books were too easy. DS8 enjoyed the story, he learned some new stuff (like sets), and it eased us both into homeschooling. We made it as far as Fractions before we stopped (DS found the Bridge sections to be too stressful, so we are on hiatus.)
Regarding religion, yes, the religion is throughout all the books I've read. But I don't think it's too overdone, and it does expose DS to an aspect of our culture that he wouldn't necessarily see (we are not religious at all).
As for price, we just bit the bullet and bought them. But we've got DD7 occasionally using them too, now, so that helped justify owning them. I have seen them for sale on some of the homeschooling-swap groups, but I bet they go quickly.
We have all the books through Beginning Algebra, although we stopped using them formally after Fractions. That being said, at least once a week I see him reading one of them on his own.
I think one reason DS likes Fred is because even though Fred is brilliant, he's pretty naive. Fred makes mistakes all the time, he's constantly learning, and he's non-threatening.
