There are quite a few on here that have one (including me). It works fine in inland lakes, and quarries, assuming you have a modicum of visibility, and decent light.
You may find, however, you'd have better success if you replaced the convex outer fisheye lens with a flat lens like many on here have. There are number of choices (i.e. Eyeofmine, Mako, and my recommendation, the BlurFix from Snakeriver (google it). Without the flat lens, the vids are a bit blurrier than need be under water.
As for the mounts, I tried the wrist mount, and the camera flooded... fortunately, I caught it early. There were apparently a few bad o-rings that went out... The headstrap cam works well, if you modify it with a chinstrap to hold it on. I used a length of 1" webbing, and triglides and it worked perfectly. I'll post a pic tomorrow.
You might want to "like" the GoPro facebook site. Lots of good videos posted there.
