The Amulet of Locking seems pretty useless to me. If I want to practice security, I'm not sure relocking a chest at 5 and then picking it (on repeat) would be my preferred method.
It is handy for Security training though... for roleplaying.
It's also neat to lock a door, so that an angry NPC cannot open it and chase you. Then you can heal yourself, and unlock the door when you're ready to fight again.