IMO such sticks range from useless to harmful. The ones with lines that allow divers to measure things underwater are nice, but:
Please don't destroy the environment ( break corals, stir up the bottom or harass rare critters) with these as we see too many divers do.
Also note to dive guides: your guests will not enjoy a dive where they hear banging all the time. By doing this, you not only unsettle other human beings in the water, but also wildlife. Big fish will run away from you. A diver who wants to see what you point at will look at what you are pointing within a short time. A diver who does not care about what you want to show him will ignore banging at best or resent it and not want to dive with you again...