Like the extra episode of "Onegai Teacher", the extra episode of "Onegtai Twins" is a pile of poop, a blatent excuse for fanservice. In fact, this extra episode is even worse than that of "Onegai Teacher", which is an impressive feat given how sh*t the latter is.
The reason why I consider this to be worse is because in their eagerness to mass produce fan service, they completely threw character consistency out of the window. They've changed Karen from an introvert into an extrovert filled with incestual lust, and thus destroyed what little character integrity the entire series had. For an extra episode, that is in my opinion, one of the worst you can do to a series, and had I cared about the series to begin with, I might have been quite pissed. But as it is, it's no big deal, cos the series sucked bad anyway :P