My older son is 10 and has developed a bit of a love for these books, as my constant battle to find things he enjoys reading continues. I tried him with some of these on our kindle, and he actually said he liked them and enjoyed reading them but would prefer the physical books, so I picked up a couple of the more recent books in the series.
These books are a good transition from less wordy graphic novels that he typically gravitates towards - dog man, mr. wolf - into a more traditional chapter type novel. Slow progress on his reading path, but at least progress.
He's enjoyed these books and typically reads them to himself when he goes to bed. He's read them cover to cover and I'll for sure buy more books in the series this Christmas.