Bip39 Checksum. Firstly you need to retailer it SEPARATELY from a seed. Getting your seed and also your passphrase in exactly the same location defeats the goal of having a passphrase to start with. What constitutes a "superior wallet" is one that has clear, very easy to access documentation on https://bookmarkworm.com/story19013453/bip39-https-linktr-ee-bip39-top-guidelines-of-bip39-passphrase