Slaves was a joke

Cirrus is supposed to be that ship that comes in with three or four other ships, who sit at the very edge of the solar system as the resupply & command/communications (beam coms are less detectable than broadcast or FTL transmitter)

Cirrus is exactly that- a really big powerplant with some crew quarters and stuff stuck around it, with big engines and a big gun pointing forward. Very expensive, and they're likely to be really rare. But when you see that same task force appear on the edge of the system, and that ship suddenly disappearing, you're likely to start panicking, because omgwtfwasthat. Then the task force will either disappear or something will suddenly explode with a beam of energy spearing through it- likely through a weakspot.

Hard to detect, but then again, if you've got a planet with defensive satellites and a fleet in orbit with a standing flight of fighters and bombers constantly patrolling, the Cirrus will have a hard time moving quickly without giving itself away.

That, and it's kind of like a superweapon. Really expensive, because of all the expense for building it, servicing it, and keeping it working. But hten again, it can spy on most people without being detected and even shut down a dreadnought, by, say, shooting the engines and possibly hitting the reactor, causing any warship to recognize the ship was just severely and irreparably disabled, and activate a self-destruct to keep technology and the ship itself from falling into enemy hands. Ta-da, but then everyone'll be chasing the new-revealed Cirrus, who'll be rushing out of the gravity well and to safety. 

And Cirruses are more of a pre-battle scenario. Say, most people have it as a offense-vs-defense, but perhaps there's a pre-battle, where you can take your Battle Points and spend a few of them to use beforehand, or perhaps just a pre-battle amount of battlepoints. They may or may not show in the actual battle, but you'd be scouting so you'd know the defensive forces.

A Cirrus has really really advanced stealth systems, a really big powerful reactor, three rather large engines, somewhat weak shields, another shield that tries to trap and escaping residue from engines/laser/reactor/stealth devices, and a big gun that kills stuff by channeling an insane amount of energy in one shot, which leaves it too overheated and pretty fried, so it has to cool down and get a bit of engineers' attention before it can fire.