The main difference with Mastadon is tha with Mastadon you have a single node that you get your federated feed from, and that verifies your identity. Therefore if your node operator doesn't peer with some other node, you wouldn't automatically be able to communicate with users on that node.

With nostr, your identity is just a pubkey, and you can publish to / read from several nodes simultaneously. So if some node refuses to puplish certain content, you can just get it from another node without having to create a whole new identity.