At the 77% cacao mass level you’re starting to traditionally get into the more bitter level. Here you’ll often get a bit more of an ethanol edge that some people will find unpleasant. It would be unwise to make sweeping statements, however, as how bitter a bar will be at this level will depend largely on the type of cacao bean used and the conching time.
I had hoped for more from this Bouga Cacao bar, but at least it had a very interesting rustic nature that you don't often I get to try all that often. It was also slightly spoiled in transit so just be aware of that.