You know, most of the times the problem is really solved, and the inventor just loses the time and money he could invest on some unsolved problem.

Yeah, some times an extraordinary invention just changes the scope of the problem, or solves it so much better that "good enough" stops being enough. But if you have one of those solutions, you probably know it, and should also know that the problem is solved - how can you revolutionize a mature market without knowing it's mature? (That'll probably be the case here if that brush really works.)