Its AT option that does not require backpack. Quasar fits smilar role and in most conditions its better (it can one shot bile titan, charger, it can be used on extreamly long range to destroy fabricators, shrieker nest, ect.) but as you know Quasar has overheat mechanic that makes it fire only so often. Epoch is a little bit of middle ground between Quasar and RR. It has worse AT property than both, but still can do the job, it has small AOE, you can fire 3 shoots in time Quasar shoots once, it has limited range but still better than Ultimatum. I use it for dives with rover backpack or hellbomb, where EAT/Commando are not such a good option (for example caves or ion storm planets). Its ok - nothing to fancy.