Zapp seems to do relatively well with it in his Tundra =P
Forward guns are great. They're hard to aim, yes - you either have to Ram your opponent while shooting, be an ace gunner, or be shooting a very large target... but because of that aiming difficulty and limited firing arc, forward guns are able to be balanced with much higher damage and efficiency rates than other heavy weapons. The lib cruiser forward gun does more damage than a light mortar, costs less energy, and has a higher projectile speed.