The major pro for me is that I know exactly how it is encrypted end to end, and have control over how and where it is stored, and can move the storage as I please, all entirely for free.
Otherwise it's fine. The multiple Vaults is great to share passwords among family or maybe your co-workers. It has features like TOTP and supports many types of other fields.
4/10 on usability 10/10 on its core feature set. Probably a 9/10 on osx.
There's a slightly easier way - escape out of the basic auth dialog box, open the 1password menu which will be showing you the website you're on and select 'Autofill', and then reload the page (ie Ctrl-R) and the basic auth is supplied from 1password.
Not great, but easier and faster than copying in username and password fields manually (and with keyboard shortcuts available to do each step it can be quite fast).
From 1password comments I believe the limitation is because Firefox does not allow 1password to interact with the auth dialog box (which isn't strictly a bad policy from a general security point of view).
Having said that, Bitwarden is a big pain in the ass. I still can't open the main window when I'm in private browsing window.
Unlike the other options, it's a deterministic password manager. This means that you don't need to sync anything, and there's no risk of losing your password database. As long as you know what website you're signing in to, and remember your one master password, you can regenerate all other passwords.