Short answer: A credible glucose metabolism supplement admits when its finished formula lacks independent clinical testing, rather than implying ingredient research proves the product works.
Why ingredient research and finished-product evidence are genuinely different things
What exists is general research on individual ingredients such as mulberry and cinnamon — which is not the same thing as evidence that this specific product works.
What to check regardless of which specific product you're evaluating
Whether the brand discloses full ingredient amounts and whether "broad promises" covering multiple unrelated health areas are treated with appropriate scepticism.
💡 Worth knowing: if there is a benefit, expect it to be gradual and modest, and to vary considerably between people.