Hypomimia, a reduced facial expressiveness in Parkinson's disease, is clinically relevant yet difficult to rate consistently. We evaluated the usability of CAPtion, an iOS application that supports standardized, session-based retrospective hypomimia ratings from camera-based facial recordings, enabling structured scoring across multiple independent raters. Six Parkinson's specialists completed one predefined rating session and subsequently filled out the System Usability Scale. It achieved a mean SUS score of 91.7 (±6.8), indicating excellent usability and suitability for scaling to larger inter-rater variability studies.