Kara no Kyoukai: Mirai Fukuin - Extra Chorus is (hopefully) the last hurrah of the Kara no Kyoukai series. In essence its a series of shorts that is about giving some closure to the cast of the series. It is a bit of fluff to enjoy and nothing more. Not that this is a bad thing, but still, it should be called what it is: a bonus feature. Of course, that is basically in the name (Extra Chorus really does give that away).
The artwork is good, the writing is decent for in essence three short bits of around ten minutes each, and really, it is just the cherry on top for the fans of the Kara no Kyoukai series. In itself, it adds very little. But overall, it is just a short and rewarding experience for people who know the characters. Otherwise, it is just a waste of time. There is no realy point in examining it any further than what it is. Still, it is not a complete waste of time.
Alas, there is only so much you can write about while keeping things spoiler free, so I think its best left at that.