Chord recognition. How the arranger reacts to one or more keys pressed and released in the designated chord recognition area. This is one of the two defining characteristics of an arranger, the other being style pattern transposition. (You could consider notes added above or below the melody note as a third.)

My other micro niche is rubato styles (similar to Yamaha free play.) A "free play" style can be configured for ANY arranger that has sync stop, or "arranger memory" and a retrigger or autobacking parameter.

With a simple but carefully configured rubato style and MIDI out, you can use the chord recognition fingering on one brand of arranger to drive the style engine on another. This permits a "best of breed" approach.