The apartment is OK if you're just looking for a place to sleep and you're looking for nightlife, we stayed here for 3 weeks so we didn't have the best experience.
When we arrived the apartment was untidy and dirty, we had to wait for an hour for them to clean it. The host promised us a 300mbps Internet connection "right in our apartment" but it turned out to be a slow connection shared between all the apartments, I work from home and I specifically asked for this so this was a big deal. He also said it was a quiet apartment but the noise coming from both behind the walls and the street can be ridiculous, especially during weekends.
As everyone points out, the toilet makes a lot of noise and you have to wait a while before using it again, also the shower drain is kind of clogged. Furthermore, there's just one window in the entire apartment, which might not be important if you're staying for a day but it can be frustrating if you're staying longer.
Finally, the location is great if you want to be in the center of Madrid, there are lots of stores and the subway is just a few blocks away.