From what I can tell, the kanji index is useful if you want to quickly want to mark a number of kanji as known, or block from studying, but for more complex things like setting mastery or making lessons in bulk requires the Japanese Index.
It would be useful to be able to import a list kanji in the Japanese Index like you can in the Kanji Index. The Japanese Index has a search, but it seems like it cannot handle a list of kanji.
