Hmm. I've heard less than complimentary things about beam fighters in general; I just figured having mobile PD platforms might be a boon. I do like the idea of having dual-role fighters, though. It's worth a shot, at least; fighters are cheap, and if nothing else they're decoys I guess. Thanks for the thoughts guys.
I used them extensively in my no missiles game, and they're workable but micromanage-y. You definitely need large numbers to swamp a prepared enemy force and sand through enemy armor. In my experience, 100 fighters do a lot less damage than you would expect 100 guns to do.
The biggest problem with beam fighters honestly seemed to be the fire control range. Speed was easy, thanks to the 4x bonus, but having any kind of range makes for a bulky fire control. However, an interesting twist of turn order can help this; fighters always move after normal ships, but before precursors. This means against precursors they have to have range at least equal to the precursor speed x 5 seconds, and preferably longer (since the accuracy falls off quickly). Against NPRs you can reasonably expect fighters to close to 0 km and hold there, so fire control is less of an issue. Unfortunately, I have a lot of trouble finding challenging NPRs to fight in my games.
I ended up with basically three types of fighters. The first and simplest was a gauss armed fighter; since it needs no reactor and gauss can be minaturized, it's the smallest (and therefor fastest) you can make a beam fighter. Unfortunately, since it has essentially no range it's mostly useless against precursors, who are your most likely opponents early on. The second type was a laser armed fighter, using the reduced recharge rate to make a 2 HS laser and tiny reactor to make room for a longer range fire control. These were fun but expensive fighters, and the most effective against precursors, but don't inflict much damage with their low fire rate. The third design was a railgun fighter with slightly more range than the gauss fighter, and a lot of damage; unfortunately it was heavy and required improved armor and engine tech to even be practical.
I didn't get that far, but I suspect at a certain tech level gauss fighters come to the forefront again; unlike lasers and railguns it gets increased damage (fire rate) techs, and against NPRs a tiny, fast, short range fighter could be nasty.