If you think it's too cheesy to put it on a ship with a single weapon battery and a pile of defences, just throw it on an unarmed ship, the smaller you can make it, the better. The targeting formula will revert to the normal pattern, but you'll still get the bonus from the module across the fleet.
I don't see that there is a huge advantage compared to just outfitting all capital ships with defences. True, the space you use for defences could have been used for weapons, but a sufficient defence means that your fleets may be able to battle more enemy fleets before requiring repairs.
If all your capital ships have defence then any combination of your ships will work fine against most attackers and you can carry on if you lose one or two along the way. If only one ship has defence then you either need to have a spare kicking around nearby or you have to retreat.