There was an article on HN earlier this week about PBKDF2 iterations[1]. The gist of the article was that adding iterations to the key derivation function doesn't actually increase the entropy of a password all that much. No matter how much education and encouragement they're given, some users will choose weak passwords, and those passwords will be crackable even with any reasonable number of DF iterations.

This was good support for 1PW's 2-key solution, since one of the keys is randomly generated with a true 128 bits of entropy, no matter what password the user chooses, a compromise of the service's data store alone will mean the user's vault encryption key is uncrackable.

[1]: https://neilmadden.blog/2023/01/09/on-pbkdf2-iterations/

Disclaimer: I'm an employee of 1Password.