my TL;DR, as a western classically-trained amateur musician largely unfamiliar with Indian music: Harmonium (a small reed organ) is widely used in Indian classical music but its use is controversial because it doesn't allow for the fine adjustments in pitch (roughly analogous to the D#/Eb distinction discussed here) that is seen as central to most/all Indian styles.
https://news.ycombinator.com/item?id=31476078
my TL;DR, as a western classically-trained amateur musician largely unfamiliar with Indian music: Harmonium (a small reed organ) is widely used in Indian classical music but its use is controversial because it doesn't allow for the fine adjustments in pitch (roughly analogous to the D#/Eb distinction discussed here) that is seen as central to most/all Indian styles.