I didn’t read either book, but it sounds like it may be a decision for each parent to make knowing their own child.
I just wanted to comment on the Holocaust comparison. Although it is a different question, as some posters explained above, I would agree that parents may want to monitor at what age their kids read which Holocaust books as well. It is not a matter of something necessarily being appropriate/ inappropriate. It is simply that children at different stages are emotionally and psychologically ready for different information. Some more graphic Holocaust books may not be appropriate for preteens or even young teenagers.
The books mentioned above may be wonderful, serve an important purpose, etc, but that doesn’t mean it is appropriate for every child at every age.