Both the reviews section and the footer say that testimonials are opinions and do not guarantee you will achieve the same outcome.
It is a plain reminder that a testimonial describes one person's experience under their own circumstances. Their diet, sleep, age, activity and baseline are unknown to you, and so is whether anything else changed during that time.
It is also the brand's way of stating that the testimonials are not promises.
Take the disclaimer at face value: read testimonials as stories, not predictions. The product's own results for you depend on you, and the way to find out is a simple, honest trial with a baseline and a log. Keep your expectations modest and your decision date inside the refund window.