Bip39 format https://www.anobii.com/en/01000289012ff9b293/profile/activity Regardless that it makes use of BIP32 method you are able to nonetheless import BIP39 seeds into Electrum wallet. Also apart from BIp32 there is BIP44 Model which some wallet use for your technology of seeds. The amount security does a passphrase increase? A BIP39 passphrase appreciably https://www.hometalk.com/member/176312665/elva1377050