Hey! Yeah, Seed Signer has done an amazing job.

The coin flipping method to derive a mnemonic phrase essentially serves the same purpose as dice rolling, which is to manually generate your mnemonic phrase. With the coin, you toss it and record either a 1 or a 0. Eventually, you end up with a sequence of 12 or 24 binary numbers based on that random outcome, and you then match it to the corresponding word in the BIP39 list, where mnemonic phrases are sourced from.

And the passphrase essentially acts as an extra layer of security. By adding a passphrase, it protects you if your mnemonic phrase is compromised, since the private key is completely different. Using just the mnemonic grants access to one private key, while using the mnemonic plus passphrase grants access to another.

Hope that's clear, and sorry for going into so much detail!