I play pretty slowly and take my time. On Nightmare with trials it took me 13 hours to complete and I didn't do everything. The DLC is story driven and focused, like a main mission in the main game, and it is exceptional. The pacing, the cinematic design, the music, the atmosphere, the drama, it is the epilogue DAI deserves. Well worth the $15-20 IMO.
As for the goodies, I don't personally use sigils, but I really enjoyed the trials that scale enemies to your level and give them extra abilities. I wanted the main game to be more challenging, and I got my wish. The extra ability upgrades were also a nice touch.