Flat is well located, in a calm street but close to trendy areas. Good dimensions. If you have a big luggage, climbing 5 steep stairs is no fun. I can't imagine with kids.
Flat is not fit for the winter. It was cold and humid. I stayed in many other places in Barcelona and never was that cold and humid. On the first day, there was heavy rain and water dripping in the room from the wooden window.
Also I experienced miscommunication with Marta (who doesn't live there. It is just a rental). Had to wait for cleaning lady 30' at the building door "because usually tenants confirm arrival time from the airport" (but Marta did not ask me to) and when leaving, cleaning lady arrived 25' early while I was still packing and using the bathroom because Marta gave her an earlier departure time.
Overall, it's an ok flat with its advantages and disadvantages - you just have to know them before making up your choice.