It is a universal fact that customers play an important role in business growth and“Happy Customers” are assets of the business. On the other hand, it’s a fact that we all get influenced by the opinion of others to some extent. In the same way, testimonial videos will definitely generate more leads than a website with no testimonial page.
It should look very natural. The ambiance, setup, make overs etc everything should look real. The more closer it is to reality the better will be the impact.
The industry you're in and the audience govern a lot about whether testimonials are of any value at all. There's quite a lot of study on the subject. I recommend you look at some of the experimental research that MECLabs does on "what works."
figure out who your target audience is. and find someone who exemplifies that and who have had a genuine fantastic experience with your product. let their passion and appreciation for your product show through.