I've spent 5 days at Mabel's place. The apartment is very central and some of the main attraction of Barcelona are less than 200mt from the door step. Great the Picasso Museum and Barceloneta Beach. Nearby are not missing a big supermarket and many local restaurants. Almost a week spent there without the need to get any public transport as everything was at walking distance from the flat.
Mabel is very nice, the communication with her was great and I've got many tips on how to visit and move around the city.
The flat is located at the 4th floor of an historical building, very silent considering how central it is. I would for sure recommend Mabel's flat to my friends.