Of course it's better to have a real password manager, but for most people, who don't or can't be bothered setting this up, this would be a huge step forward since they anyway use the same email and the same password everywhere.
Never, ever, re-used passwords for anything you value.
Most people re-use not only the password, but also their email. This is the worst combination.
If you use an unpredictable, unique email address, and use a secure password. Even if it leaks on one site, the attacker has no easy way to predict what your email address is going to be on any other site without having access to the list of email addresses.