But everyone knew this already. They only work in very special cases of imperfectly competitive markets, e.g. where each firm faces the exact same downward sloping demand curve, e.g. the monopolistic competition models used by the macro literature.
How does other people using an unrealistic assumption make the use of an unrealistic assumption any better?
(also, demand heterogeneity is not the only issue Jamandreu points out: "The problem becomes more acute if there are adjustment costs of any variable input (e.g. labor) because they constitute a non-ignorable part of the input prices and the own marginal cost")