I'm starting to think that the "sweet spot" for the flak is too narrow. It detonates shortly after it's arming time. It doesn't have too much of a window to be effective, even when paired with the Hadies or mercury cannon. Either shorten the arming time or lengthen the range to make this window a little bigger. Either that, or increase the ammo mag to where you can lay down flak like it's the battlestar galactica (a bit of a hyperbole there), but I think that would make things a little too similar to the mortar.
It's currently out-shined by the Artemis missile, which will not only kill stuff, but also strip components, and do it with more accuracy and rounds in the clip!