Jet packs are basically giving the scourges a reliable fof. (I'm assuming that we are talking bout the 4 DL configuration here) Basically you move 12, and then since you can't shoot, get to move a guaranteed 6 inch move in the assault phase. Just an interesting question, (I don't have my BgB with me, lent it to a friend and it's way over due to come back home) but if scourges fired w/ their DLs would they be able to move 6 in the assault phase? If so, that is a bit to over power I think, although I could use it quite happily.
Now, if we use the 4 SC configuration, then I think Jet packs are way over powered, seeing as against swarm armies, they'd move out from behind cover, fire off 16 shots, and then move back behind cover again.
A bit OT, but is there any assault oriented unit in the game that has Jet Packs and can fof? If so, who, so I can target them soon into the battle.