I wouldn't put this in the list of Avi's best books, but it's not terrible, either.
I wasn't impressed with the reading; the reader did voices and all, but the reading style was reminiscent of children's audiobooks of the '80's - everything is overly-enunciated, the pacing is slow and deliberate, it's almost pandering. It made the characters feel stilted and unbelievable.
The over-use of little pearls of wisdom - and I am far too lazy to research whether each of Fabrizio's cliches were translations from actual Italian sayings of the day or if they were made up - and the term "with your permission" became grating to me.
That being said, it's still a quick, fun mystery. I think it would appeal to boys and girls and would be good for just-emerging-from-reluctant readers.