In both manga the heroine has to dress up and put on makeup since she's a popular model (in Brilliant Magic) / singer (in Charisma Doll) and becomes a different person. However she has to be careful not to let anyone find out her true identity.
They're both about being discovered and becoming famous while hiding your true identity. Both girls have limited self-confidence and have trouble saying how they really feel. Though there are some differences, if you enjoyed one manga, you will definitely like the other!