Didn't Semirhage have loads of copies of the male a'dam? Besides, it's too big a detail to have been put in for no purpose. It's fairly obvious that someone will attack a lightside channeler while wearing the medallion, to much panic and WTFery. Then either a circle of Aes Sedai will round the corner and overwhelm the medallion, or there'll be a terrible heartbreaking scene where our lone channeler deliberately draws too much of the Power, defeats him, and dies. I mean, the early books never shut up about how dangerous it was to channel too much of the Power, and yet we've never seen it happen. Why?