I also have a HS friend who loves this series and recommended it to me (she HS through a christian charter school, but they are allowed to pick whatever curriculum they like, the school just organizes activities for them and helps them if needed). Sam's club currently carryes the K, 1st and 2nd grade books for a good price. So, I picked up the K one and we will probably just use it as a supplement and pick and choose what looks interesting. It has a nice of, "classic" stories/poems that I probably would not have normally expose my children to. I did see some complaints of ppl on amazon though, b/c they said some of the stories were kind of violent or something. However, from my experience any of the, "classic" stories are often not edited to be PC in today's stds, so I can see why it would rub some ppl the wrong way. I guess for stories like that, I'd either just not read them to my kids if I find it inappropriate, explain to them why the story is like that, or fill in controversial parts with my own version.
My dd likes to look through them. (Got them at the thrift store for $1.) Where they came in handy was when dd was worried about getting behind the schooled kids (yes, she's only 5, but she has a bit of competitive streak, not my fault I swear.) So she looked through the K and 1st grade one, realized that she wasn't missing anything and moved on. They are great on a cold rainy day in winter to just browse around, like a little kid encyclopdia.
Are these the What Your...Needs to Know books? I got the Kindergartner one. Neither of my sons are in K but it was an interesting book. We have looked at it together and we have read a few stories from it. It covers everything and can be a helpful resource!