I recently saw a news report on how those devices don't work.
They said that the current wasn't strong enough to give your abs a good workout. It's supposed to work like the machine that a physical therapist uses, but it's just too weak. When they attached that machine to someone's abs, it pulsed so hard that it made the guy's entire body actually shoot up in a forced crunch. I actually had that hooked up to my quad when I was rehabbing my knee a few years back, and I sure as hell wouldn't want it attached to my abs lol
John