Simply put, I trust the password manager. Recently, however, I have considered uninstalling that plugin and using only the desktop version of the password manager -- and then copy/pasting username/pw from the password manager to websites.
One reason I don't do that, though... is because having the password manager as a browser plugin guarantees (?) that the password it presents to me is for the site I am visiting. If I end up on a webiste with an IDN that was chosen very carefully to look like my bank's domain, my password manager plugin won't present me with a password -- which will trigger my paranoia.
If you can't tell, I wrestle with this decision pretty regularly...