The apartment is in a good location. The building is not so quiet though, and neither is the street. The name "Marco" is actually a cover for an agency, where they have a relatively complex check-in method (each and every person staying in there would have to download an app and register in through there - to me this was really lacking practicality for a weekend-trip). The people working for the agency have been quite helpful, nevertheless all in all it was very impersonal. It would have been of course an entirely different story renting the apartment directly from the owner or at least a single care-taker.
I found the apartment a little dark, but all in all, it is more or less clean and well equiped. We were six guys for a long weekend in Madrid, it was alright for this purpose, but I wouldn't recommend it for families.