I think the core difference is that "Eagle Cash" is not centrally managed - the balance is actually on the physical card itself. I imagine the MS cards is more

I think the core difference is that "Eagle Cash" is not centrally managed - the balance is actually on the physical card itself. I imagine the MS cards is more of a "central account" that is accessed when you swipe. I guess each "Eagle Cash" terminal has a certificate, and whenever you credit/debit the card, the terminal adds/subtracts the amount on the card, signs the new balance with the certificate, and then this can be verified at any other terminal. In other words, you can't modify the balance on the card unless you have the secret certificate, which is only present on the authorized terminals. If you try to modify it yourself, you can't do it, because no other terminal would accept the card unless the balance was cryptographically signed with the cert. That's my guess for how this works, at least. I wonder if each terminal has a unique cert that can be revoked if it is compromised.