Few questions:
1. [solved] How does it work? I couldn't get it from the website: 'go/' is not a real DNS-resolved domain but some host alias?!
2. [solved] If 1 is true, how do you want to target smaller to medium sized companies which just have G-Suite, Slack but no real intranet/private net where you could create this host alias easily for the entire staff? Guess I got it wrong, so I am happy about a technical explanation/architecture.
3. How is the business model's defensibility? What's hindering me to set up the same with some open source repo, write a Chrome extension, add a nice landing page and hire a sales force for SaaS enterprise sales?
EDIT: ok now I fully read your post and got my answer for 1 and 2 but how should this work on mobile where you don't have extensions?