We stayed at Koni's apartment only for 2 nights (beginning of June) while passing by Barcelona. The reason I would recommend the place is because of its central location - only 3-5 minutes away from Plaza Catalunya and the Rambla in one direction and Park Cuitadela (the best) in the other. Also there is a metro station right next to the apartment.
The place is clean and I really liked the way the check-in is handled - you will get a code for the front door and another one for a little safe box with the apartment key. This is very convenient when you don't know exactly when you will get to the place.