Yes, the book is several flavours of funny. Let's look at the list again.
"Unfailingly funny." - Arthur Smith
“One of the funniest stories you will ever read.” Daily Mail
“Very funny.” Independent on Sunday
“Join Me is the kind of book I love: effortlessly funny, painfully accurate and entertaining to the very end. Brilliant.” Mike Gayle
“Very funny and, in its own way, an affirmation of the generosity of the human spirit.” The Independent
“As you’d expect from Wallace, a lot of it is very funny. Hideously, out-loud-laughingly funny.” BANG Magazine
“Hugely funny.” Word Magazine
So it's official. Join Me, the book. It's funny.