I use OBIs when shooting BPCR and F class as required by the rules.
My other main shooting sport is IDPA in which pistols are kept holstered except when on the course. No flags required or even feasible. But leave that sucker in the holster until it is your turn to shoot.
I have only shot on a couple of those rental ranges with the clerk "range officer" overseeing operations and they did not require them. Just stand back from your open gun while others were downrange.