I stayed 3 months in Buenos Aires and Federico's apartment made me feel right at home! It is as described in the post, cozy but spacious, with plenty of light, and has everything you need. The building pool is nice and clean and I spent many sunny sundays there! Location wise, it's walking distance from Plaza Armenia and Plaza Serrano, where all the bars and shops are, and is also around the corner from Santa Fe, where you can take about any bus to anywhere you wish.
Also, while Federico was not in town during my stay there, he made sure his friend took great care of me from the day I arrived to the day I left. His mother too was always available to help solve any small issues that may have come up along the stay.
All in all, everybody was highly attentive and I dearly recommend Federico's apartment for a memorable Porteño experience!