The aim of this study was to evaluate and compare the impressions of older adults with mild dementia/MCI (mild cognitive impairment) and people with schizophrenia towards the usability of GRADIOR (version 4.5) and their user experience (UX) with this computerized cognitive rehabilitation program. The impressions towards the usability of GRADIOR and the UX of 41 older adults with mild dementia/MCI and 41 people with schizophrenia were obtained using the User Experience Questionnaire. Older adults with dementia/MCI had more positive impressions than people with schizophrenia. Both agreed that its quality was lower in Dependability. GRADIOR meets users' needs and preferences but needs improvements to ensure they feel more in control when interacting with it. For people with schizophrenia, other aspects of usability and UX need improvement. Usability and UX evaluation allow the verification of technological acceptability and functionality, and to identifying specific improvements for each user group.