I can see your issues and having broken a collarbone (clean and healed) and a shoulder (pinned and plated) feel your pain.

Talk to your doctor explaining the insurance thing. Getting a bone pinned is not a big issue and if done OK, can be left in for the rest of your life (most doctors won't take metal out unless it's causing issues or for religious reasons).

No, you don't set metal detectors off in an airport- there is not enough metal.

No you most often cannot feel plates or pins through your skin or muscles.

Yes, pinning does work, however of course it is surgery so there is risk.

In NZ I don't think bone stim is available, so it's always surgery. Sometimes I wonder if doctors often push new things too much. Get a third opinion if you feel you need to, but make sure you explain your situation about the insurance. Doctors should take into account people's financials as well in a treatment program.