Sébastien Page has a good comparison between one of the more feature laden and expensive cross platform password managers and Apple’s built-in Keychain:
To me, it is pretty obvious that 1Password is much more powerful than iCloud Keychain and is well worth the price.
I use both and each has strengths and weaknesses. Keychain is free while 1Password can cost $3 per month forever.
If you’re an Apple-only kind of user, then iCloud Keychain is great, but if you are working on other platforms such as Windows, then your iCloud Keychain data won’t be able to sync over… In comparison, 1Password is available on Mac, Windows, Android, iOS, and all popular browsers
The article has some misinformation regarding password generation, but the reader comments are worth a look.