Yup. I used one for a while. It's just like most any other fishing gimmick, some days it'd work, some days it wouldn't. But then if I hadn't been using one, some days I would have caught fish, and some I wouldn't.
Spend your time with your string in the water instead of messing with gimmicks. It'll pay off.
The two best fish finding tools we have are (1)Our brain, and (2)a pole. Figure out how to use them and you're catches will be far above the rest.