Privacy: NIP-60 proposes a new event kind so it would be visible that there's activity. The ecash coins themselves are encrypted but the number of coins (which is visible) *might* allow correlations (realistically speaking, I'm not concerned by this). Example: "Martti seems to have 10 encrypted coins on this relay... I'm guessing that's around 10000 sats but who knows, could be 10, could be a million".

It might make sense to use a different key pair for NIP-60 that's derived from your OG keys, but that would be harder to agree on.

NIP-61 is about using these ecash coins for zaps so the whole idea there is to be public.

 

 In this example the eCash is publicly known to be locked to Martti’s npub? Is it possible to make these similar to silent payments [1]?

1. https://bitcoinops.org/en/topics/silent-payments/