They give up as soon as the airline resists
We brought Flightright two separate cases after already contacting the airlines ourselves and getting nowhere. We accepted the hefty success fee because we thought we were paying them to handle exactly that friction. Instead, they declined one case and closed the other as soon as the airline rejected their demand. Both cases had a strong and clear legal basis. It leaves me with the impression that their service mainly works when a passenger hasn't already contacted the airline and the company pays after receiving a standard letter. If the case requires actual enforcement, even with a strong underlying claim, my experience suggests they may simply walk away. That makes it difficult to see what the substantial fee is meant to cover. I wouldn't use Flightright again.