This domain is supposed to be a Debian FTP mirror, but it doesn't behave like one. Instead of serving software updates, it redirects to a web hosting company, Nautile. That is a major red flag. Even if the redirect is a leftover from an old configuration, the SSL certificate is for Nautile's domain, not for ftp.nc.debian.org. That means any secure connection to this server fails.
For Linux users looking for official Debian repositories, this site is not trustworthy. A legitimate mirror would have a valid certificate for its own domain and would not redirect to a commercial homepage. The domain has been around for years and isn't on any blacklists, but the technical misconfigurations outweigh those positives. I would stick with the main Debian mirrors or known official mirrors.
When assessing any FTP mirror, always check that the SSL certificate matches the domain you're connecting to. A mismatch like this one means you can't be sure you're getting genuine files. The question "is ftp.nc.debian.org safe" has a clear answer: not in its current state.