My two cents.....Whether I am spearfishing in Boynton, or spearfishing in Jupiter, I am pulling either a torpedo buoy with flag on it, or a traditional flag..this is not so much because of my interest in boaters seeing me--it is my interest in making it easy for MY BOAT to see me, and to stay in my area ( and play chicken with any jerks that look like they are intersecting my path).
I did plenty of dives in the old days with Frank Hammett, where none of us spearfishing would tow a ball--Frank would just figure out where we would come up--most of the time
And there were times when we were floating on the surface for a really long time, waiting for him....holding up a speargun with a flag on it.....but again, this is to get picked up.
I would never "trust" a flag or an smb to function to protect me from moron boaters...There are huge numbers of jerks driving boats, that do not give a rat's ass about watching for floats or flags,
and this is very unlikely to ever change....For these people, when you are doing your "safety stop", you are listening for boat motors...
when you decide to come up, it is with a deflated bc/wing ( something that instructors should start teaching) , and you are scaning 360 even before you hit the surface--and you are ready to jacknife and dive down should one of the morons be headed your way.
If you have a boat watching your flag/position, then this is nice, but it does not mean you don't need to watch out for yourself.
I'll say this another way....divers should assume that there are dozens of criminally negligent boaters out on the reef they are diving on, durring any given day they go out. If you take this to include that some boaters may think it funny to "almost" hit you on the surface, then YOU will probably make choices in your surfacing behavior , that will keep you safe.
If you trust in boaters being nice or caring, you are making a huge mistake with your own life, and those who might follow your lead.
Regards,
Dan V