I'd replace the benefit, yes, even if it's not there by RAW. No matter whether you fire 3, 6 or 10 bullets with the action, you get the benefit of 3 bullets for Bullseye and no defense penalty effect.
As GM, I want to only allow these with Narrow Bursts, still gaining the Narrow Burst damage benefit, but that means SA-Bursts cannot use this and I dislike nerfing it like that. I would allow combining them with a Narrow Burst for bonus damage, though, since that means you're turning your Simple Action into a Complex Action for the same amount of bullets.