Re: why trust a third party?
What's wrong with using a Libre Office spreadsheet protected (AES encrypted) using a sentence (upper case lower case and symbols) that one memorises?
1) It's potentially vulnerable to key logging.
2) It's inconvenient.
I do use locally encrypted files for more sensitive stuff, but it doesn't come close to the convenience of LastPass for logging onto less sensitive websites (like this one). For example you can search your LastPass vault by keyword to find a website if you can't remember the URL and it will go straight to it and log you in; your spreadsheet can't do that. Really important passwords, like online banking, I won't write down anywhere.