The extra turret offers bigger DPS so its damage output becomes the best among the Epsilon T1 tanks. While it may die to Lasher Tanks, Opus is very useful at destroying structures and miners. I can't say it for sure, but the double barreled Opus Tank has better DPS than certain soviet and allied tanks.
Opus can also be used to carry passengers to different locations, while it is still able to fight back. You can use this to weaken structures so a single engineer can capture them instead of 3.
And as Jem said, the role of the repair unit in the Epsilon arsenal is taken by Stinger + Engineer.
Shadow Tanks can detect cloak, but it isn't basic technology. If you want to harass Epsilon miners, but you are at T1, then Shadow Tanks aren't really an option. Besides, some double barreled Opus Tanks with some Stingers can do better job at harassing than Shadow Tanks and that unit composition is somewhat cheaper than going for pure Shadow Tanks.
Edited by Petya, 04 January 2015 - 09:37 AM.