The restricted key means you must work closely with your locksmith to keep a single copy of your key, exclusive. Not only will the key be completely custom and exclusive to your business, but there will also be branding and conversations between locksmiths to create a unity of discretion and protection.
This means that if the person ever tried to go to a different locksmith, they wouldn’t be able to get a duplicate because the key will be restricted and branded by the locksmith you are working with.
This greatly minimizes the possibilities for getting copies of the key made because the number of people who could interact with the key is significantly reduced meaning that as long as you track the copies of the key, you are tracking the actual number of those keys in the world.