That doesn't help you much if you're starting out. You have to trust somebody and someone has to point you to something.
If it's a specific browser extension or a web page that you can run after you've cut the internet doesn't really make a difference. Note that vanity-eth.tk points out that you don't have to trust them and how to ensure that the private key stays private. But that needs some knowledge and that's certainly not for everybody.
This is why most crypto web-apps have a browser-extension form; you can check in your browser extension list to verify which version of the extension you have, and so know that it’s safe if someone you trust has already audited that version.