Is this really that useful though?

It's very useful if you don't use a password manager and/or reuse passwords.

The most useful part about it to me is the API. You can tie it in to Active Directory to blacklist all hashes that appear in any breach, plus expire/force a password change if any user on your domain uses a password that has been in a breach. It completely eliminates that vector from threat actors immediately.

So yeah, I would call this intensely useful.