What should you do with used Dexcom transmitters?

What is the right thing to do with used Dexcom transmitters? Are they OK for regular trash or should they be saved for those electronics recycling events?
If you Google, there’s an ad for a company (lifeline direct dot com) that offers to buy them. I’m wary. Does anyone know if that’s legitimate?

People that buy them replace the batteries. They then sell them, but it may be fine line as to being legitimate. Definitely not if they were selling as new.

The people that send in dead transmitters are technically selling/giving a prescription item, which is not allowed. (But with dead battery, is it no longer an RX item?)

The people who buy them probably have low income or no insurance or no coverage/high deductible insurance.

There are many that replace their own batteries, and several posts here with YouTube videos.