Just the fact that she's John Cassidy's (from Fallout 2) daughter won me over, but beyond that Rose of Sharon "Cass" Cassidy is a fun companion with great voice acting and dialogue that I repeat still to this day,
Cassidy is arguably one of the best companions you can travel with in Fallout 2 for combat, especially if you give him a Gauss rifle. The hardened wasteland veteran that got old and settled down as a bartender in Vault City unless you go there and ask him to join you. The con is his prejudice against Lenny the ghoul, another companion you can travel with, and will insult Lenny if you travel with both at once. The pro is he also hates Myron, the sadistic drug supplier/slaver/sex predator, and Cass will endlessly insult him if you end up recruiting Myron to travel with both of you.