I'm not totally sure I understand the Assist Maneuver. As a Maneuver as opposed to an Action it seems ready to abuse. I hope I am wrong but It sounds like all the players can assist 1 player to shoot an NPC? Like PC's 1-3 say "I am assisting player 4" and when it's player 4's turn he gets to fire with an extra 3 boost dice?
Seems overpowered to me, I dunno.