NRTL listing is not “required” by code for anything that is plugged in, because the Code is only about permanent installations and construction standards. If you want to risk your life on something that the manufacturer didn’t think would pass testing to any standards that apply here, so they didn’t even try (or tried and failed) that’s up to you.
In SOME cases, homeowner insurance policies may have “fine print” statements to the effect of giving them an out from paying for damages as the result of a fire caused by unlisted devices. They would have to prove it of course, but that increases your risks in deciding to purchase the devices.
NRTL listings also help protect the resellers of these devices from indemnity over manufacturer defects. So if you buy something from a brick-and-mortar store and it starts a fire, the store can deflect blame by saying “It was a listed device, we did our due diligence so talk to the manufacturer”. That’s why you will not see unlisted devices being sold that way. But when you buy them on-line, the on-line seller is just “facilitating” a transaction between you and the cheap crap manufacturer or dealer, usually in China. If something goes wrong, the on-line seller says “Caveat emptor”, an ancient legal precept that means “buyer beware”; it is incumbent on the buyer to understand what they are buying and what risks are involved. Then if you go after the Chinese supplier, they are shielded by their government against liability claims. You end up screwed and holding the ashes of your disappointment.
