Guys, do check your local laws, sometimes the specific size and construction of the flag is different from "stuff that's sold on the web". Even within the US, a flag can be perfectly legal in 49 states and still illegal in Florida.
Personally I'd like something about six feet square that followed me without a tether, and had a couple of Phalanx guns on it, set to maintain an automatic hundred yard perimeter.
Here, ANY dive flag just attracts idiots in boats or jetskis who want to come see what the colorful thing is, and whether they can take it home.