It's written in a very simple way, far from being academic and suitable for programming classes and newbies.
Moreover is totally centered around FPC and Lazarus!
Hello Riccardo,
I read the sample chapter and, it looks good.
I have a suggestion (for which I don't qualify): currently your book has no reviews. I suggest you give away about 6 copies of the book to Lazarus/FPC experts in exchange for an honest review. It should be very easy for you to locate half a dozen experts that can give a fair review.
I believe a couple of good reviews from recognized experts would be beneficial to promoting your book.
HTH.
PS: I don't qualify because I code exclusively to the Windows API, in other words no RAD. My editor is my "RAD".