Well I wrote the Limante article for Warp Rift, and ive used all escort fleets so ill share the top three positive and negitive things that my near decade of using them has taught me.
1. Decide right away weather or not you want them to *finish* or *screen*, two entirely diffrent roles, for two entirely diffrent escort types. IE: The cobra is great at screening due to the ordinace and cheapness with which you can purchase them. But they arent more them mediocre in finishing due to the number of variables involved with their torps, and 1 mesely weapons battery.
The more likely finisher will be the Manta/Firestorm/Sword/Nova/Gladius/Any other gunship escort you find. The reason being is very likely in just 2 or 3 of these things you will find a full cruiser broadside's worth of firepower with far more flexibilty due to their very nature and manouverability. You may have trouble with blastmarkers and celestial phenomena if you arent careful with your caps, but escorts are far more forgiving in speed as well as manouverability. Thus allowing them to skirt the edge or hang out in the rear and charge forward to cripple/kill anything previously weakend by your Line ships.
2. These suckers are fast, lets face it 30cm + is a pretty great opportunity to cause some havoc and open up opportunites that capitals simply cant find, minus the trecherously good slaughter that is, or the necrons too I supose but ive got other reservations with them that dont belong here. With that speed comes a wealth of tactical options, and while most of them dont use the escorts to their *intended* role in the fleet, they are still there to throw off your opponents own plan or just do something fun. Ever seen 3 corba's board a devestation and actually cause a crit? I managed it once, next turn they all died to AB's but thats neither here nor there the fire was caused and much annoyance was had when he couldnt put it out.
3. They pretty generally are paperthin, minus marines and necrons usually, and cant go toe to toe with their more contemporary cousins in the caps while expecting to win. But due to the sheer numbers of them you can crank you, you could hypotheticly give that enemy cruiser those easy vp's in order for your own larger elements to secure others that it might have interfeered with. True you arent likely to meanigfully hurt the opposition in this case unless you have a 6 str squadron of heavy escorts (IE: Those costing in the 40pts + range) and their firepower tapers off unerringly quick. But this tactical option can save your bacon by spliting their firepower when they need it concentrated the most. And while you are depending on them to take the bait, you could always lock on and make them remember what escorst can do unmolested.
Now for the bad stuff.
1. They are far to vunerable to attack craft. True the recent revised FAQ's and general outlook have made them more survivable, but they are still laughably vunerable to it. The only way to secure some safety is also a detriment to their again, weak surviability. Base to base contact can aleviate ac problems, but then exposes you to enemy gunnery to wreck havoc with you.
2. Unless you use them as an outrider formation away from the main fleet, usually not a good idea, they will have their speed dictated by much slower caps. Thus they usually cant get far, fast, without breaking the cohesion of the fleet and destroying your chances to use them most effectivly. Thus their own pace of battle unlike the caps, is direceted by friendly action, rather then the enemy's.
3. Lastly, they are pretty far down on your totem pole for Special Orders, because unless its a 6 str escort carrier/Cobra squadron(or equivilent ordinance boats elsewhere) you generally want your caps to go first and likely one of em will eff things up by keeying in the wrong radio channel and the admiral will spend 15minutes screaming at the incompetent moron for doing so. Thus they are a shotgun weapon system in all but the rarest cases, used effectivly at their best for one turn, and an after thought from then on.
None of the above are definitive, I must have/never have escorts in my fleet points, because its all due to your own style of play that dictates that. But when I pull out my 120 escorts to tangle with his 10 caps, my opponent begins to wonder if he can possibly kill enough of them before I L/O and take out almost assuredly 3 of his ships on the opponening alpha. True brace can muddle things up, but thats why you hold off overwhelming firepower on a single target and basicly whittle it down with 1/4 or 1/3 of the total you could have put against and to force a brace, if they dont, hurt them more until they do. Dont ever tell them they should brace, let them keep shooting them selves in the foot.
Either way, those are the main points, but definatly not the only ones to be made where the tin cans are concerened. I love em, some hate em, but they are undeniably useful little buggers if you take the initative and make them react to you.