Testing the product with users is a more practical approach because it targets potential consumers directly. Firstly, you need to conduct usability testing to determine the immediate problems with the UX design and interaction.
This way, you will be able to see first-hand how your target audience uses the product and obtain some performance statistics.
If you want to gauge how the product will perform long-term, you can conduct 'diary testing.' Ask the participants to log answers to specific questions about the app for long periods so that you can make a definitive conclusion on the software performance.