This is a fantastic series! I'm using this nonfiction collection with my sixth graders this year and so far I love it. The stories are really high-interest yet easy enough for kids to understand. Lots of great vocabulary that can be figured out using context clues. Also, the personalities profiled in this book really are quite eccentric and I think the kids will love reading about them. People profiled include Snowflake Bentley (a guy who photographed snowflakes), Black Bart (a "nice" bandit), Johnny Appleseed, Vincent Van Gogh, Salvador Dali, and many others.
The assessment resources at the end of each story are also quite useful (main idea, vocabulary, inferences, finding facts in the story, etc.). I highly recommend this to teachers because it seems like a great way to teach kids to read nonfiction text, which is often something kids struggle with in middle school.