Ooooh, I hadn't read about all of those other projects. It seems that the ones minted by Casascius are unique not only in their concept but in their fame and history. That's what separates it in value from the others.

I would prefer metal coins too since they give an air of further solidity. However, these days, you can just put a hardcover over them and send them off to a safe house where they shall stay undamaged until the end of days... or the time when they're sold. We could say that preference is the only "real" difference between them nowadays, since they'll be equally durable, and just as valuable if they have a similar collector value.

I don't get the point of buyer funded ones. If it's a collectable but it's modified by the buyer, it doesn't make any sense at all for future buyers. Perhaps for someone who just wants one saved in their home with a cover on it. Like a Rembrandt that you know is a Rembrandt but you had to 3D-print it. It's unique to you, but you printed it, so it loses value for others, but it's just as pretty for yourself.