Thanks TH. You and everyone else answered my question. I'm going to get my wife and I each one of the annoying devices.
She and I were diving a pinnacle this weekend shrouded in a kelp forest. Water temp was a balmy 58*. Visibility varied between 15 and 25 feet when you could see past the kelp. Single file is best when picking a path through the stalks with a quick buddy check by lead about every minute or so. I was lead and she was swimming about three feet above and behind me to avoid getting kicked and stay clear of my bubbles. At one point immediately after one of my buddy checks she swam right into a big furball of fishing line that I never saw. She was banging on her tank with a carabiner we were trying out as a tank banger. I just kept on swimming, not realizing the problem or hearing her trying to get my attention. She freed herself and was just swimming back into view when I did my next buddy check. She flashed me an okay and I learned about her problem when we were back on the surface.
It wasn't serious this time, but you never know. We really haven't had a problem in warm, clear water. In the kelp though, in a 7mm wetsuit/hood, seems you need something louder due to the buddy positioning, increased focus by lead, and possible sound absorption by the kelp and hood. Needless to say we won't be using the carabiner again. And unfortunately that big fishing line furball is still out there. If she had been able to get my attention it might have been possible to get it back to the boat.