I’ve tried it. Late last year when I was at the mall Christmas shopping I bought one of those belts for $7 or something off the clearance shelf at one of those "As Seen on TV" stores. When I put it around my waist, it did make my ab muscles contract a bit, but it’s more like a timed reminder to flex your abs. I tried it on the underside of my cock, on my pad and on my perineum. It just stung — kind of a sharp pinch, or a pin prick. I suspect the problem is that the bc muscle is fairly internal and just shocking the surface doesn’t do much.
There is a whole genre of "e-stim " sex toys like these that use a little electric charge to stimulate your parts somehow. Maybe it feels good to some people, but I suspect it’s a very expensive and inefficient way to do kegels.