User testing, simple flow testing

I am going to run a user testing for a bank in order to evaluate ''be our customer'' flow. Which starts with collecting basic information then connecting with a representative to finalise the application. The flow is very simple, it has only one CTA for each screen and dropdown selection & basic input text fields to collect information, hence I believe task completion rate etc is not right criteria to focus. I would like to investigate how the logic of questions to collect basic information laid on the flow and how confident the user to give information on that flow to be a customer. What type of methods you would do?