There is nothing more convincing than a good testimonial, so a testimonial video must ooze authenticity. So absolutely no reading, no scripts, no teleprompters. That being said, the thinking will need to be done beforehand in terms of what questions will get the best answers. The person being interviewed will need to be relaxed and enthusiastic, so there will almost certainly need to be several takes. I always use at least two cameras on tripods and a third handheld - which enables me to get close-ups and different angles, and sometimes an surprise element.