Am I understanding it correctly? This is a GPS that somehow (???) broadcasts your location to marine radios within an 8 mile range.

I'm assuming it displays the coordinates on marine radios ... somehow? Is that a standard thing for marine radios?

Is 8 miles enough when out on open waters?

It would seem that a PLB would be a much better safer choice to protect if things go terribly wrong.

Do they make PLBs specifically for diving? I could see putting a regular PLB into an Otterbox or similar, but I'd wonder if the flotation factor would be too great. I'd hate to dive with a little box constantly pulling up on me.