I ordered these two books from my library (thankfully in paperback) for the Teen Zone. There seem to be few reviews out on the Ye Yucky Middle Ages series, but I found one that said these books were for grades 5-8 and other that said grades 7-9. I figured they would be on the low end and entertain some of the six and seventh graders. But, I am a want-to-be Medievalist (that's what my undergraduate was) and I thought they looked fun and worth a try.
I read through both of them, they do have some interesting information, but they are very much an introduction to the Middle Ages for someone who has barely heard of them, has never been to a Ren Faire, but does enjoy history. I think some sixth graders would like them, but I would give them out two fourth graders as well. They are entertaining, a bit silly and would be perfect non-fiction for the right kids. I send them down to the Children's room, where I am sure they will be checked out many times.