My 7 - year old has finished the entire set of the A to Z mysteries (including all the super editions). The super editions are lengthier and more satisfying. I started reading them because I wanted to find out how good these mysteries are and after I started, I finished the entire set myself. This will be a common review for all the books in the set (so please forgive me if you see this repeated under another book).
First of all, the mystery part of the book is fairly simple for an adult, but I can see how it can keep a kid engrossed. The characters are playful, around the same age as my kid now, so are very relatable. Yes, there are some characteristics which can be a little irritating, but they didn't really bother me too much as to take away from the stories. The other con is that these little kids are left unmonitored in many of their adventures (I am not a helicopter parent, but it felt a little strange, especially when they are out of the country altogether).
That being said, now what I loved about the stories -
1) Most of the stories are based in different cities, and sometimes different countries, so the travel perspective is amazing. We, as a family, love to travel and every time the kids in the books traveled somewhere it made the story more exciting to me (as well as my kid). My kid had comments on how they went to Key West and later Washington D.C "just like us".
2) There are strong characters of both genders, the villains are of different genders as well, so the stereotyping is considerably less (there was a female pilot in one of the books that stood out to me) and I love it that girls reading the books have some good role models. I would always like more female strong characters shown ofcourse :).
I'm sure my kids will be enjoying many more of the author's books in the future :)