Bird-shooting with an open double-gun is not uncommon in my neck of the woods, mainly wing-shooting waterfowl under flight-paths. However, hunting DG on foot is an entirely different matter.

A single spear-grass seed or tiny twig on the flats of a properly-made DR may render it unable to be fully closed in an instant, or closed sufficiently to be safely fired. Indeed, the problem may not be immediately apparent and even if the shooter realises what has happened, the business of clearing the obstruction while facing down a DG charge could very easily be fatal.

What's more, the second barrel, the oft-touted raison d'etre of DRs for DG, would be equally unavailable.

Double rifles simply must be closed when stalking dangerous game.

Other than that, I agree with the other posters above: flicking a tang-safety forward as you mount a DR should be so instinctive as to be a completely unconscious action. Extensive practice with automatic-safety double shot-guns is probably the least expensive way to achieve this.

Of course, the real trick is remembering to re-engage the safety immediately if for some reason the shot is not taken! ..and this applies to the Krieghoff decocker as well.