This tool may be useful for newbies, but certainly not for experienced Wikidata editors, as no one in their right mind would use P854 in references. In case anyone else is not aware, this tool is unhelpful when it is being used in references because it relies on the incorrect (from the Wikidata point of view) P854 property instead of the existing Wikidata external identifier. I don't recommend it to anyone until the obvious major errors are corrected.