Never use a fishfinder rig with an eel. They go together like Jim Beam and grape soda, with no ice (don't ask me how I know this). You do not fish eels as bait (i.e. like clams or bunker), and therefore a fishfinder rig is a terrible choice.
The best way to fish eels is just like a plug, only slower, about 1/4 - 1/3 the speed that you'd fish a lure. Tie your running line to a barrel swivel, and tie about 4 feet of 50-lb. leader material to the other end of the swivel. Snell a large-ish hook (I like a razor-sharp 7/0 hook; sharpen it yourself, because most hooks are not sharp enough out of the box) to the end of the leader, and then hook the eel through the head, so that it is swimming naturally (green side up, white side down) when you are retrieving. Though you want to do it slowly, you want to keep the eel moving while you're fishing -- otherwise (eels are masters at this) the eel will probably ball itself up on your line.
The other trick to eel fishing is not to get the herky-jerkies. If you feel a fit, don't swing the rod like Harmon Killebrew -- give it a five-Mississippi count, and then drive the hook home when you feel a tug. If you try to set the hook at the first hit, all you'll do is yank the eel out of the striper's mouth.
As to their efficacy: eels almost always work. They will not catch bass if there are no bass around -- nothingwill -- but if there are bass to be had, an eel is as good a thing to use as anything. And they are also bluefish magnets: there's nothing like shelling out $15 for a dozen eels, and having blues turn them all into cigar butts in a half hour.