Back in the early 60's when I was diving in the caves, springs and quarries in Missouri, most of the divers I knew were using some form of a regulator necklace. Since we were diving in caves and springs without the safety advantages of octos and spare air that are available today, the necklace was a critical piece of equipment from my perspective. Although I still see the regulator necklaces on the online websites, I have never seen anyone use one in OW even though I can still see some benefits of using one. Is there some reason divers are not using them other than they have an octo readily available, or is is just not cool?