How about Questions, Options, Criteria?
Q1: How about note input?
O1: Vectors (Drawing), note keys (Cover, Glove)
C1: efficiency, hardware dependence, piano experience
Q2: Ease of use without being able to see?
O2: Braille alphabet, sensing button limits
C2 : effectiveness, usability, easy to learn
Q3: How about getting feedback from the application?
O3: Audio instructions/responses, haptic feedback, vibration on errors/alerts
C3: user satisfaction, effective communication, trust and security
Q4: How about getting used to (or learning to use) the application?
O4: Audio tutorial, previous experience with real piano keys, Braille alphabet knowledge
C4: accessibility, user satisfaction, learnability