If you are wondering whether to stay at the apartment I would just do it! It has the perfect location, situated closely to a street with tapas and pincho bars. You can walk up to Monjuic- which is a must! And get the metro that's a 5 minute walk from the apartment to anywhere that may be further away. I would suggest that one of the days you stay around the local area as theres some lovely cafés, patisseries and markets surrounding the area paralel and Poble sec.
We had a fantastic time in Barcelona, made better by our lovely airbnb. Thank you!