I love kokuji in general, but I love the seldom-used kokuji for metric measurements in particular. Taking a roughly phonetic indicator of the unit in question, e.g. 立 for litre, and then sticking in a modifier for the SI prefix e.g. 毛 for milli- is an elegant system, much like the Chinese system for naming new periodic elements (radical indicating state at room temperature + phonetic compound based on IUPAC name) but overloading existing characters for the base measurement and then having to create new characters for each prefixed variant, plus assigning an english loan word as the onyomi for each character proved unpopular in the end, and the katakana form of these loanwords won out, leaving these kokuji consigned to novelty and occasional shorthand (it added a certain dense flair to my chemistry notes in college). Maybe if new characters were created for each base measurement, or maybe an approach closer to the current Chinese method of metrication would have proved more popular, but then we wouldn't have these fun hybrid characters.