Fili and Kili are crazy good in a deck running the Fellowship contract. As long as you have one of the brothers and a copy of A Very Good Tale, you can play him, go grab the other, then exhaust both with AVGT to potentially drop two more allies. The result? Four unique allies toward your goal of 9 at the cost of 3 only resources! Of course, they are also integral pieces in a Dwarf swarm that wants to get to 5 as soon as possible.
The biggest downside is that Fili (and Kili) are at their most exciting and powerful when they enter play. Afterwards, the stats-to-cost ratio is actually below average (though Dáin Ironfoot and Hardy Leadership can help with that). In sum, it's great fun to bring them into play, and then they provide only decent contributions to your board state afterwards.