@Gixl Nothing unusual at all. The onahole market is huge, has tons of variety and exists for at least 20 years now. It's more unusual there aren't more guide books like these.
I find the variety fascinating, particularly in the realm of mildly-to-extremely inhuman features -- suction cups, ribbed tongues, et c. I also appreciate the ones for specialty tastes. Wanna fuck a fat girl with a huge clit? Page 83. Wanna share an onahole with a shota, so you're bumping into his cock at the end? Page 68 has you covered. Wanna grind into featureless silicone? Check out page 79. And so on, whether you want to insert your balls or whether you want to fuck an actual toilet. Hurrah for creativity.