Super idea. I made a diving flag buoy sometime ago but never really used it since it was terrible. Your clean system made me rethink my old one (threw it out). Copied yours ( will all due credits when asked) and now I have both a MOD buoy & a diving flag buoy all in one. I just change the flags.
Also, I modified yours a little. I cut it in half; threaded the ends; treated them crazy glue to harden them; and connected them using a rod threaded connector ($2.30). Helps with storage in a cockpit bench and out of sight when not there.