I am getting closer and closer to needing such sights myself. But not always appropriate on truly old vintage guns. At least if done unobtrusively it makes such firearms usable and not just another safe queen gathering dust in some collection of 300 other safe queens.

No close up side on photos of the ribs to show how obvious grooves are.

A three barrel set is quite unusual, 2x shotguns, 2x rifle barrels, and a combination set. Damascus barrels.