You are correct that Screen Hero still works and all, but it is technically "dead." No one new can sign up for the service. You can only use it if you already had it setup. I would personally consider that "dead" if it's now closed off for anyone to signup with. It's not like you can recommend this as alternative to what Slack is doing with their screen sharing.

On https://screenhero.com/login they even say "New signups are closed while we integrate with Slack." - I consider that "dead."