How do they work, do they have a private key engraved?
It so how do you know the designer/maker wont sweep them?
No key, just a novelty gift. They have no value other then what the receiving party would be prepared to give for it.
Awhile back I read a thread somewhere on here that some company did just that.
i.e ...actually engraved the priv key with a sealed hologram or some such thing and sold
the various bitcoin valued coins they fabricated.
And guess what ended up happening?
Not too hard to figure out...lol