Chocolate keys are door openers to the customer
The apartment door falls loudly into the castle. The resident stands with the newspaper under his arm, but without a key and possibly not adequately dressed outside in front of the door. There is either the breakneck entrance through an open window, a balcony door that is only leaned against, or a friendly neighbour calling the locksmith for help. Anyone who has been "rescued" by a locksmith in such an awkward situation will certainly be surprised if he is given a chocolate key with a company logo as a customer gift to calm his tense nerves. Which at the same time makes the anger about the mishap go away.
Take the opportunity to permanently bind this customer to you with a small but high-quality promotional gift. If they want to install a security bar to protect their home or flat, they will remember your company before looking for competitors in the Yellow Pages or on the Internet.
But even if you are celebrating a company anniversary, you should give the sweet promotional items, be it as keys or as chocolate bars with your logo, as giveaways to your guests on the way or you send the small promotional items with the next customer mail.