This pdf presents a new race, that should not exist. It's entirely unnecessary. However, it's very well constructed and I have a soft spot for weird things. Seriously, I love flumphs and I've been a goblin fan boy since I started playing 2nd edition and Magic: The Gathering. Yeah, I'm a goblin hipster. I liked them before Paizo made them cool in Pathfinder.
Statwise Goblumphs gets bonuses to Dex and Wis and a penalty to strength. They are humanoids and have the goblin subtype, but they are also considered aberrations. They honestly get some pretty cool features (that I don't want to spoil, because you should buy the pdf).
Do you need this pdf? No. Should you buy it? Well if you like oddball stuff like me and are a flumph aficionado, then abso-fricken-lutely.