I have one inconspicuously hidden under a sticker that will unlock one of my smart locks. Needing to unlock my phone is what prevents me from using it that often, though.
It is fun to use it when friends/family are around, and see them go "Whaaaat?!"
With iPhone shortcuts, you don’t actually read anything off the tag, it just recognizes it and runs a shortcut that calls a home assistant entity (least that’s how I do it).
Your NFC reader on your phone reads the data on the tag whether you believe it or not. If you have writeable tags, someone can just overwrite your tag rendering it useless to you until you fix it.
I have an NFC tag which has a homeassistant action written to it, and it’s also set up in Shortcuts as an automation. It works on Android, and iOS! So no, you can’t override the shortcuts trigger.