The ensemble cast if nicely diverse, and it's fairly easy to keep the characters straight. Maya's sister is a great addition, and it's nice for younger students to see older girls they can admire and ask for assistance.
The fun illustrations scattered throughout the book also make it easier to identify the characters, and add a fun facet that might help attract readers to the books... and help make them coders!
There are very few books of any kind that include coding as a key plot element-- Gene Luen Yang's Secret Coders is the only one that comes to mind. There are a lot of books that include groups of girls doing projects, so Girls Who Code will be popular with readers who like Simon's The Cupcake Club, Kimmel's Forever Four, or Singleton's The Curious Cat Spy Club.