One.o9.de is a German domain that gives almost nothing away about who operates it. For any website, but especially one aimed at people in Germany, the lack of an Impressum (the legally required business disclosure) is a real problem. It suggests the site may not be operating in line with local law.
We also found no about page, no social media profiles, and no record of the site in the Wayback Machine. The technical setup is fine, fast loading and a valid certificate. But that doesn't help answer the basic question: who is behind one.o9.de, and what do they want from visitors?
If you're considering interacting with this site, whether signing up or sharing information, the lack of transparency makes it hard to know if it's safe. With no track record and no identifiable owner, the safest move is to wait until more is known.