As someone who just recently moved into the V ranks, I was told that blowing the whistle was "redundant" and to let the table sound the horn.
My reply to that was always, "The reason I did it, and still do sometimes, is at below V level, the table is usually not that good and doesn't sound the horn, therefore the whistle is needed."
Took some getting used to.
I like what some of the others have said too.
Bottom line, as was said, "When in Rome...."