This one just wasn't for me. It's not one I'll be keeping around for my boys, either.
From reading around, it appears this book is a prequel to the HULU show, Moone Boy, which I haven't watched.
To start with, there's a great deal of footnotes, which bugged me to no end. You'll be reading along, and come to a word with an asterisk beside it. Knowing there's a note at the bottom of the page about that word, you'll feel the need to go ahead and read it. Then you'll have to go back and settle into the story again. Even if you resist reading the footnote immediately, you'll at least want to read it before going to the next page. These footnotes happen very regularly, sometimes multiple times per page. It was just super annoying, and made it impossible to settle into the story(for me, anyway). That said, without the footnotes, I wouldn't have had a clue what was going on half the time. Some of the words are used in America, and they seemed to be defined purely for humor, but there's lots of Irish things within the story that most of us Americans wouldn't know anything about. While I don't mind learning Irish things, I don't care to this way.
Next, while I'm not naive in the world of sibling rivalry(I had a sister and a brother, and I have 3 boys of my own....plenty of rivalry experience), I didn't really care for some of the remarks in here. At one point Martin struggles to get the image of his sister's weird mole, back acne, and tufts of shoulder hair out of his mind. Turning to physical issues for humor typically bugs me. I've worked hard with my little ones to not laugh or point out physical things/issues about people. Sometimes it's a live and learn kind of thing, but I wouldn't hand over a book like this to them. I stopped reading about halfway through, but from scanning through, Martin even offers his sister's boobs as bait for a bully problem at one point.
Due to the female "disrespect" within the book, I wouldn't recommend this to girls(at least). There's also gross stuff. At one point, a man holds one of his nostrils, sucks snot back into his nose, and then hocks and spits it on the ground. ((gag)) The books almost lost me completely right there. Showing it to my husband, he just shrugged in a carefree manner, so that kind of thing apparently doesn't bother the male gender as much as it does me(even as a young child). He didn't find it funny, though, thankfully.
Lastly, I didn't care for the profanity in the book. It seems like it's getting more and more common in middle grade books. I even have a few middle grade favorites with some here and there. Between the profanity and the slang and even some more mature things within the book, though, I was just surprised with this being in the middle grade realm.
So, if none of that bothers you, sure, give it a try. I'd be lying if I said I didn't laugh several times! Still, I won't be adding to my sons' bookshelf, nor could I comfortably recommend it.
*I was provided an ARC, in exchange for my honest opinion.