I think what makes this book work is that Bertie is constantly coming up with and carrying out crazy ideas without much adult interference. This rings very true for my experience with my boys as they grew up! They always wanted to prove themselves against their environment, and they kept impulsively following one crazy scheme after another.
The only thing that kept this book from getting a five star from me is that it lacked any sort of heartwarming moments. I wanted just a touch of sweetness or lessons learned etc. throughout, and I didn't find that. However, that may just be my personal preference. I certainly think many young readers will enjoy the crazy adventures Bertie has!