One thing I really like about the iOS Teacher app is the inclusion of a slider for grading (something that is sadly still missing from the Android Teacher app, but that's another story).
(Image taken from the official Guides pages)
I'm shifting more to using Rubrics for my various assignments, and while there are times where I'd like to use ranged values and/or free-form comments, so far I haven't been because I grade primarily from the Teacher App and it's a bit too cumbersome compared to just putting in a bunch of different rating scores to choose from.
One thing that would make grading ranged valued criteria or free-form rubrics much more effective on the app would be if each applicable criteria had it's own slider similar to the slider above (which disappears completely once rubrics enter the picture).