If the user-agent string is to be trusted the latest version released in June is still based on chrome 65.x like you said... :/ it's not terrible but not great either.

However they do claim to backport security patches on their front page so it should technically be secure.

I suppose it would take a lot of repetetive effort going through the same process to pull apart chromium each major release, so perhaps they settle on backporting patches in between larger breaks.