This flat is very easy to find with one street from Llacuna subway. It is clean and well-equipped for a long stay and has iron, hairdryer, all required kitchenware, etc. The location is great - 10-12 minutes walk to the beach, and this beach is clean and more calm than the Barceloneta one, ~30 minutes walk from Sagrada Familia; while the neighborhood itself is quiet and relaxed.
The overall experience is great, I would recommend staying there as it more than worth the money.
Little about cons:
The building has relatively thin walls so if your sleep is kinda sensitive, this can be your problem - my wife woke up several times because of the ambulance sirens on a street or kids shouting on a starcase.
The air conditioning works great and is a bit of rocket science - it is very powerful and requires a precise configuration (however, for many people this can be an amazing feature).