or it is better to to create 12 words recovery phrase along with an extended passphrase?
I
recollected the case with the Trust Wallet browser extension, where weak PRNG led to a serious vulnerability, namely, hackers were able to exploit this flaw and steal users' funds due to poor SEED generation.
Since no one can predict which wallet may expose the flaw in SEED generation, adding a custom SEED extension with an extra phrase would provide the additional layer of security for your wallet.
Personally, I always use a passphrases to extend SEEDs on all my wallets and strongly recommend everyone do the same.
Although I've already used it in some hardware wallets, I always use seed phrases of 12 mnemonic words, as explained by some here, you don't need more than that, and I can also add a passphrase BIP-39 to increase the level of security according to the size and complexity of the passphrase.
Moreover, 12 words is easier if someone wants to memorize them (never forget to make physical backups, memorizing the mnemonic is just a plus).
The passphrase is very important, because even if the generated seed has low entropy, I can increase the security of the mnemonic by extending it using passphrase.
For passphrase generation, I recommend using 6 random words or more. Random words of 6 words have, for example, the same entropy as a password like "#\KL`@cZ3W*-", I usually think that 8 or more is great.