Good thing some tapos do have alternative firmware like thingino.

You should still treat it as radioactive waste. Protect it and protect yourself from it - segregated VLAN, no internet access, just like you would do with official firmware.

If you call up your contactless payment provider, most will send you a physical device that will do contactless payments on its own, for free even. You can tape it to the back of your phone, or anywhere else for that matter.

Also, your phone doesn’t need to be connected to the internet for contactless payments, anyway.