Insider is a local assistant that runs on the owner’s computer. After you sign in with Google, it can read and send Gmail, manage Calendar events, search and edit Drive files, read and write Sheets and Docs, and read Contacts — only when you ask it to.
It is not a public website and not a multi-tenant service. Google data stays in your Google account. Access tokens are stored only on the owner’s machine and are used to call Google APIs.
You can revoke access at any time in your Google Account permissions.