I think the biggest is simply having access to your data on non-apple devices and non-apple browsers. I.e. using it in Chrome or Firefox or whatever browser you want, as long as there's an extension that supports the browser it's likely available.
You can store a lot more data in Bitwarden as well, including custom fields, so you aren't stuck with just a username and password and optional 2FA. With Bitwarden you can do security questions, a notes field, etc.
Sharing with family is another big feature. Sharing your cable login, wifi password, streaming services, etc.
There's a whole list of them, but I think those are sort of the top 3 for me.
Right, but I often leave notes in my login items themselves. If the account doesn't use an email address to authenticate I might just put the email address in so if that email ever gets shut down I know which accounts need to be migrated, as an example of why I might do that.
I tried bitwarden, and went back to 1Password. My ecosystem needs to be a bit independent for apple, just in case Apple starts acting like google, and locking users out of their accounts forever. The apple keychain has a really awful interface (surprising for apple) and family management is poor.
Oh, ok I misread the original post. Yeah I have had trouble with the browser extensions for 1Password for the last few years, will probably switch to self hosting bitwarden soon.
Its nice to have something thats OS independant. Maybe you have no plans on leaving apple now, but surely you wouldn't want to rule it out ever happening in the future. Using an external password manager just means one less pain point for migrating. Its the same with any OS, or any technology for that matter.
The Apple built-in password manager is worse than the Chrome built-in password manager because the Apple built-in password manager is not cross platform. The Chrome built-in password manager is worse than the Bitwarden password manager because it doesn't support credential sharing.
