You must be close to the enemy. I think it works only against enemies, mines etc in a range <3 km. If it does, then you can see a tetryon beam that jumps from target to target. Actually, I have the feeling, that this skill is pretty useless.
I've used it successfully, but very rarely. In the Vault Ensnared I flew into a group of ships while I was chasing down a vault weaver. EM was on cooldown and they were running circles around me. So I popped CSV II and the Tholian Rep power and boom- one banking pass and they're all fried.
I'm in an escort so it's pretty much useless. As mentioned above the range is ~3km. I might have time to pop it at the end of a strafing run, but I usually fire CSV and TS at ~8km (~5km by the time it triggers) and that doesn't usually leave much for the Tholian rep weapon to work.
I tend to get some alright use out of it for taking down fighters, swarms of frigates, and other small craft that are annoying. It can also be a nice way to stop a High Yield torp coming your way if nothing else is available at that very second.
So I would also not say it is "useless" but it is not that potent either. It is just a little additional damage you can deal from time to time. Sort of like "Why not?". If someone offers to pelt your enemy with a pellet gun are you going to say no?
I use mine when I am webbed by the silly Tholians or against mines - also good when in a shuttle - , its not a useless ability and it has to be used sensibly (it will do nothing against big heavy targets but against the smaller ones, its nice to have)