They are a no-brainer idea.
It's also a no brainer (well, maybe just my opinion) that no one/so few use one because they care more about how they look than how it works.

Bayflite, can I get one soon?
Today was the last downwinder I am doing without one. In light winds and seas it's no big deal. But in serious wind and waves/chop, it's just too easy to lose your board.
It really has nothing to do with body dragging ability (I can do that). If you can't see it, you just can't find it!!
It actually held me back a ton on what I wanted to do today because I knew if I got more than 30 feet away from my board, it was history (current was ripping and chop was high). I would have never found it. My board is also dark, no handle and low profile.

I looked for Tiffany's board only minutes after she lost it.
I looked for quite a while. Never found it.
With a Go Jo on it, I am confident I could have seen it 150 yards away.