The bar is described as having very low sugar with high dietary fibre, and that is only possible because sweetness comes from sugar alcohols and intense sweeteners rather than from sugar. Sorbitol provides bulk and a sugar-like feel, while sucralose and stevia add sweetness in very small amounts. Together they allow the chocolate-coated pistachio-meringue taste to come through without relying on a large sugar content.
The practical trade-off is that sugar alcohols are not fully absorbed by the digestive tract. In moderate amounts, they are usually well tolerated, but a larger amount at once can cause bloating, gas or loose stools, especially for someone not used to them. That is why the source material advises starting with a modest amount if you are sensitive to sugar alcohols. It is easy to eat several bars in one sitting because they look and taste like a dessert, so portion awareness matters here more than with a plain protein food.
Sweeteners are one of several factors to consider when choosing a snack. If you prefer to avoid sweeteners entirely, this product would not fit that preference. If your concern is limiting added sugar, the low-sugar, high-fibre profile is the relevant feature.