The "mule" means a chip that comes from 2 sources, like this part-Silver Slipper and part-Palace Station chip.
(Refers to a mule being part horse, part donkey, I guess. I didn't make up the term.)

The chip would not be cashable in this condition, even if both casinos were open and currently using the 2 chips. So in that sense, it is worthless. Two chips would have to be used to make 1 mule, so it's not economical to do so, unless trying to mislead someone that it was a "rare" never-seen chip. The only value it would have, IMO, is as a novelty, or an example of how coin centers can be switched.

Fortunately, these don't pop up too often, but anytime you see a unlisted chip that's a metal coin center, be aware that it might be a mule.

Since centers can be switched between 2 coin center chips (making 2 mules), there could be an opposite Silver Slipper/Palace Station mule out there somewhere.

Some years ago, I was playing poker and happened to see a mule in a stack of chips I won. Since the coin centers are all metal, it's relatively easy to ring in a mule among other chips, as long as the outer color is correct.