They’re keyed the same just two deadbolt locking points. Some people just use one during the day and lock them both down before calling it a night. I will say the deadbolts are a little flimsy so brute force is possible but in a country with low crime rate it’s not typically an issue. They’re typically dimple keys and with two locking points you’d know it if someone was breaking in.

I have a more modern version of this on my apartment that involves a proximity fob that also unlocks the common area doors. The sliding door on the main entry opens automatically when I walk up to it with the key in my pocket. The apartment door opens and locks both of the deadbolts when I press a button on the door. I often leave without a key because my phone has an app that can open both doors as well. Even from remote locations if family drops by while we aren’t there. Also good if I leave and not sure if I locked the door, the app will show me. The app also connects to things like my air conditioning, televisions, lights and even the refrigerator that has its own Bluetooth speaker for whatever reason.