We have been working through the elementary (10 books) set off and on for a while now. I think we are maybe on book 5 or 6. We just read them every once in a while and DD8 seems to enjoy them much more than DD10. We've come across some religious content, but not much and it seems to be (to us) just a hint of something mentioned now and then. I don't know about the other elementary books we haven't made it to yet or the upper level books.