Religion, in general.

In high humidity regions, ya. I’ve never had issue with razors specifically, but other items.

Defender was never designed to help directly against any of these except the last one.

Iirc any cell phone is still capable of dialing 911(or equivalent) even without a sim. So id imagine carrier towers and gps could still find it. You’d basically have to keep the device in a ferriday bag. Which complicates actually using it.