Happy, excited, and six similar feeling-words capture how someone expects to feel emotionally after using a product, before they've actually used it.
7-point Likert (1=strongly disagree, 7=strongly agree)
Lin, Y., MacInnis, D.J., & Eisingerich, A.B. (2020). Strong Anxiety Boosts New Product Adoption When Hope Is Also Strong. Journal of Marketing, 84(5), 60-78.
Free access to 2178+ psychometric scales at PsychScales