Sell them, at extortionate prices, to people who need guaranteed connection in inhospitable locations. Sailors, mountaineers, backpackers, the military: all these people will pay through the nose for a powerless, guaranteed to connect, uncrackable communication method.

As for repeat custom: mirrors get broken. You can count on people to need replacements every so often. If the initial price point is set correctly and you control the means of supply then you can make a killing even without ‘subscription fees’.