Halfling Bounder is essentially a slightly more nuanced Dunedain Lookout. They have similar abilities, similar stats and cost, and were both released in the same cycle. However, the former can cancel the "when revealed" effects of any encounter card, while the latter applies only to enemies. But because Halfling Bounder needs a side quest in the victory display to trigger its ability, it is slightly more difficult to use. The end result is pretty self-explanatory: use Halfling Blunder in a side quest deck, and Dunedain Lookout in any other one. They're both solid cards, and occasionally their respective abilities can be game-saving.
While there is a side quest in the victory display, Halfling Bounder gains: "Response: Discard Halfling Bounder to cancel the 'when revealed' effects of an encounter card that was just revealed from the encounter deck."
Sam Gamgee, The Fellowship of the Ring
The Sands of Harad #5. Lore.