Choosing the first few characters of your pubkey accomplishes the same thing. It doesn't matter if other people can generate the same thing, that also applies for NIP 05.
It's similar, but NIP-05 also has the provider verify it's indeed you by having a file that links your npub to the [email protected].
If I change my NIP-05 to [email protected], clients won't show me with a verified tick, because when they check with nip05.social, [email protected] is linked to a different npub than mine.
If I change my NIP-05 to [email protected], clients won't show me with a verified tick, because when they check with nip05.social, [email protected] is linked to a different npub than mine.