Ok, I do have a little problem with teslas as they stand at the moment.
At present, they are more like electro-mines. They will be activated, and then sit there until they find something nearby, and zap the hell out of it. However, this means, if I want to, for example, clear my roof of spiders, I either need to activate ONLY the coil nearest the spider, or not want to go up on the roof for a while, without being zapped to buggery.
My suggestion would be that the redstone signal will activate the targeting system, as it does at the moment, but will deactivate it when the signal disappears.
This would mean that you could make a setup to clear an area without said area then being a minefield for yourself.
The previous behviour could be replicated either with a GUI toggle (probably more work than it's worth), or a flip-flop for activation (not entirely sure about a reset on that one, though).
I don't think that this idea would be OP, but might make the teslas a little more accessible.
Also, if you're wanting to really throw some randomness into the mix, give it a chance to electrify creepers (low, but possible). That'd mean that you still need to be on your guard.