These beams can be very, very deadly, if they hit you they don't worry about your shields, they go right to your armor and subsystems. Even if the beam doesn't kill you, it can easily take out your subsystems.
AAA beams are effectively impossible to consciously dodge. If it shoots at you, it WILL hit with at least one of the three pulses it fires in quick succession. If you're unlucky, more than one. There's just no way around it... save one. They do actually miss on rare occasions. You must be presenting the turret no movement across its field of view, so you may be directly closing, stopped, or directly headed away, and the firing ship needs to be stopped. Very rarely in this situation the beam will just shoot around you. But don't expect this to save you in a tight spot, because it's much more likely to just skewer you.
This weapon is your worst nightmare. Even a single hit can do extreme damage to you, possibly kill you outright. Make note of AAA emplacements on NTF capital ships and stay the hell out of their firing arc.
A lot of the times, a capital ship would try to finish off another capital ship using the same weapon. However, I would say it is totally useless. A good example would be the mission where the Psamtik engaged a Fenris and a Levi. The cruisers were doing quite some damage to the Psamtik before they went down. To sum up, when used against a fighter: Deadly. Used against a capital ship: Useless.
These are also quite good against bombs, thanks to their long range.
The difference between the AAAf and the AAAh is that the AAAf is for use on friendly warships, and the AAAh is intended for use on hostile warships. Thus, AAAf beams become less accurate on higher difficulties while the reverse is true for the AAAh.
It should be noted that when firing at fighters, the weapon uses a three-pulse shot in quick succession, but when firing against capital ships it fires one longer, sustained shot.