Bad actors are going to ruin this cool little device for everyone else. For every story I hear about a cool usecase for it, there's another about it being used to annoy or harm others.
I tried repeatedly to sell mine there, because I'd see some auctions for them complete. Then they told me it was definitely banned, because it could be used for (IIRC) RFID hacking.
(Fair enough. I ended up having to sell mine locally, for a lot less money than what the occasional auction would complete for on eBay. And finding a buyer locally was harder, and with much higher rate of flaking. As someone with deep frugal influences, who likes to save money when buying things, and to sell things once not really needed, I really like eBay when it works OK.)