Katia's apartment is in a very good, central location, with proximity to public transportation (RER, the metro, and Velib') and the Jardin du Luxembourg. It is small but charming, and it met my needs perfectly during my week in Paris.
The only negative I encountered, for the sake of completeness: the hall smelled of cigarettes so I kept the apartment window open at night, but this allowed bugs to enter and bite me.