The apartment is really nice and located in the middle of residential area, which allowed us to experience the local life in Barcelona. :) It's very closing to Sagrada familia (10 mins by walk). We only took taxi's during our stay, so to other sightseeing places also 10-15 mins by taxi.
We were five people (4 aults plus a baby). The space is big enough for us. All the basic facilities are available in the appartment. Small and big supermarkets are nearby.
The sound isolation is not very good comparing to the house. But during night it is very quiet. Please bring the slipers if you get used to using it inside house like us.
Their are a lot of restaurants at street of "Avinguda gaudi". The price is acceptable and cheaper comparing with the Netherlands.
Frédéric responsed us very fast by messages. We didn't have the chance to meet him, his colleague wecomed us, and he is also very very nice.
If I have to find the min point of the apartment. That is only one: the floor was not really clean, which I realized by seeing the shoes (only used inside) of our baby. We don't think it's really a problem, because we only stayed a few days. In general we enjoyed staying the apartment very well.