Google has introduced this warning for all Apps that have not been published publicly on the Marketplace. Graphus is a private app that has not been published on the Marketplace. Hence the warning.
Google introduced this warning after some G Suite Admins were tricked into clicking phishing links to private Google Apps that were 'spyware'.
The warning says "Only proceed if you know and trust the developer". Our customers (paid and trial) have been using this App since October 2016. We have been in contact with them through email and phone. They know who we are and they trust Graphus. The App is already active for your G Suite and you have been using it for some time now.