The Royal Library of Denmark has gone live with an Umlaut implementation.
They’ve done some local UI customizations, including multi-lingualization. (We hope to get the i18n stuff merged into Umlaut core).
Although at most libraries, users more often use Umlaut as a target of OpenURL linking from search platforms, rather than starting at the Umlaut start page. I’m not sure if the Royal Library’s use cases are typical in that way or not. Royal Library’s Google Scholar preferences still seem to point directly to their SFX instance, not to their Umlaut instance. (And Google Scholar makes it increasingly hard for users to find and use this preference anyhow, honestly).