"The controller chips inside the SD cards (of all sizes, whether full-size or MicroSD) are required by the SD card standard to support a low-level command that locks the card into a read-only mode, preventing any changes - either temporarily (can be switched back to read-write) or even permanently (without a way to ever restore the write capability).
This device has an ATTiny85 chip can send such a low-level command - this chip connects to the SD card, reads the lock status, shows it using the LED and allows you to toggle the lock status using the button. It supports both temporary and permanent SD card locking"
This is outside of my wheelhouse, if anyone knows if this is snake oil please weigh in and i’ll edit this post accordingly.