I'm a new player too, playing engineer. One of my level 1 achievements calls for using burst rounds to kill components. And with those, I made an odd observation yesterday (v1.3.1 already).
For one, I used them to great effect on the banshee. If it's already good at spreading fire around, than 50% more radius will make it even better, and two more rockets per volley helps as well. It already fires relatively quickly, so the slight drop in rate of fire isn't too critical.
And here's the odd part: the whirlwind gatling. It obviously has no AoE worth mentioning and will never hit multiple components, burst rounds or not... I loaded them anyway, because it makes the magazine go from 60 shots to 72 shots. And then I listened to the rhythm of the shots. And while on the banshee, or the echidna, or the artemis I was easily able to tell the difference in rate of fire... I couldn't detect any difference whatsoever with the whirlwind. It hammered at exactly the same cadence as before, as far as my perception was concerned. I even went in sandbox mode to doublecheck in a stress-less situation, and it still felt the same. Could someone please independently test that?
That would mean that you get 12 extra shots on a primary armor breaker with no penalty whatsoever. Whether that's a bug or not, at least until the next patch it seems like a decent enough option for close range. Greased rounds will still pull higher DPS in the short term, but will inflict less total damage per clip and negatively impact gun mobility and projectile speed.