It's much more about aligning the freemium window with the urgency horizon.
A two-week trial won't convert a user that's solved their issue within that window.
OBS can replicate the audio routing (though not as smoothly) though I'm not too familiar with its audio processing capabilities. I mostly see OBS and Audio Hijack as complementary products.
That said, Audio Hijack is so good for routing and processing audio that it's not even a competition, AH all day.
I've done so much mischief and tinkering with AH just because it's so easy. You can reroute audio between applications, fiddle with L/R channels and filtering, and pipe it through to others, all on the fly. I've used it for everything from being a DJ in zoom calls, to setting up presentation audio, to setting up a virtual sound board that repeated audio snippets I collected in real time from the conversation, to connecting a facetime audio call from one teammate into a zoom meeting.
There's so much flexibility and setting up the workflows is a breeze. AH hurdles the bar IMO.