At Ahrefs we are running between 130 and 170 millions sessions a day. The project started before the release of puppeteer. I can tell you the release of puppeteer saved me a lot of time. It's way more easier to keep a correct browser state using it than what was previously available. It also interacts well with lighthouse. I wouldn't call chrome headless stable or bug free (it doesn't even handle https correctly). But it's a good thing to have it available.