I can understand that, I also know more people who say they would never put something like that on their front door, and online you can find more opinions that are against it. But that's okay, everyone can and should decide for themselves what they like and what they don't.
My better half was also very skeptical at first and always took the key with her just to be safe. Over time, however, she built up more and more trust herself because it worked so well. She also realized that if it doesn't unlock automatically sometimes, she can still do it with her phone (which has never failed) or unlock it with the key after all. By now, she is so confident that she no longer worries if the key is forgotten at home (probably only because subconsciously she has our hidden spare key in mind :D...).
I believe the spare key also unconsciously helps me maintain trust, after all, nothing works perfectly forever (not even the aging brain against a key forgotten at home, even if you don't like Nuki :)).