The location of the flat is great—groceries less than 50’ away, a metro stop at the end of the street that goes straight to many key sights in the city, and plenty of places to eat within a few blocks.
The flat was also clean, but it was pretty worn: if you look at the pictures, imagine a location that is just one level more dingy than they represent. Most of the doors scrape the floor (which made them look ratty, but also made them noisy for trying to move around quietly while people were sleeping), one of the showers was completely unusable (for two unrelated reasons; both resulted in different types of flooding), and the A/C made a recurring noise (which, hopefully, gets fixed before the next guests arrive). The amenities were kind of stingy, too: no hand soap in the bathrooms, just two laundry pods (we were there for four nights), and no dish towel in the kitchen.
Overall, we had a great time in Barcelona, and we got used to the limitations of the flat. The hosts were very responsive to messages, but two attempts to fix the A/C over 3 days did not address the issue (and the shower was going to require more major work than could be addressed while we were there).