That’s a great method as it can keep the kids calm. The kids do not know how to swim.
Also, parts of the choke points are NO VISIBILITY areas with rough currents, a combination of could cause a kid to panic as they become disoriented and full of fear.
Those cassettes can protect against bumping up against rock carried by high currents in a pitch black dark. And this goes on for miles. One can imagine an overwhelming fear striking each kid as they don’t know up from down or which direction. Their lives are in the hands of the divers.