Is their story correct, that Glucoberry reduces production of SG2 (sodium glucose transporter 2)? Is the effect enough to be of significant benefit?

There can be a measurable difference, in some individuals, in the expression of this transporter, but that is not the most important thing needed to happen for those with diabetes. So, as such, focusing on one part of an extremely complicated metabolic regulatory complex makes a nice story for marketing purposes but will not have a high‑level impact on the illness on its own.