The main difference is the nutritional profile. A typical chocolate bar is built around sugar and fat, while this Bombbar bar is built around protein. It contains a blend of whey protein concentrate and milk protein concentrate, which supply amino acids — the building blocks the body uses for muscle recovery and maintenance. The sweetness comes mainly from steviol glycosides and polyols, not from added sugar in the usual sense; only the chocolate coating contains a very small amount of sugar. The bar also includes isomalto-oligosaccharides, a fibre-rich component that makes it more filling and gives it a more substantial character than standard sweets.
In practice, this means the bar can be a useful option if you want a chocolate-flavoured snack but prefer to keep your sugar intake lower. It is not sugar-free in the strictest sense, and it is not a substitute for a balanced diet. If you are comparing it with a regular chocolate bar, the main differences to look at are the protein, fibre, and sugar content.
One thing to keep in mind: the chocolate coating and the polyols can affect people differently. If you are not used to sugar alcohols or have a sensitive stomach, start with a small amount and see how you feel.