Setting up a NWBib-specific URL shortener probably would be too much overhead, wouldn't it? On the other side a hbz-owned URL shortener could be used for other projects as well. (See also this blog post by Staatsbibliothek Berlin describing how they set up their own URL shortener with https://yourls.org/.)
From https://github.com/hbz/nwbib/issues/40#issuecomment-169031473: