Well, I haven't tried Viral Shredders on the offense much - not many planets I've run into have large enough ship swarms to get non-diminishing returns out of them - but as a defensive unit they are golden. With Advanced Warp Sensors to know where the enemy is coming from, I just park my Mark I-III unit cap+ fleet of Shredders on top of the wormhole and generally come out of warp raids with a fair amount more Shredders than I went into it with. It's nice to have a reliable homeland defense while the rest of my fleets are out pounding planet after planet.
So far I've only managed to take one of those ARS, but the second one is my next priority and the third should be pretty quick after that - I just discovered what an A-Team Light Starships paired with Frigates are if you can punch them past the wormhole defenses.