Underworld Goods are given to your Companions to raise their affection level for you. Depending on your companion it may or may not effect their affection level. This page here is going to give you a run down of each of the Companions and whether or not they like this gift. For more information on the specific Companion's likes and dislikes click on their link below.
Assassin Droid Target History (Underworld Goods Blue Item)
Drayen Hyperspace Smuggling Routes (Underworld Goods Epic Item)
List of Companions that like Underworld Goods
Bounty Hunter Companions
Imperial Agent Companions
Sith Inquisitor Companions
Sith Warrior Companions
Jedi Consular Companions
Jedi Knight Companions
If you find anything wrong with the guide on this page or if you just have a comment about it please feel free to leave it below!