We (4 friends and I) had a great time in Madrid. Everything went well, meeting with Sergio was quite easy and the checkout even easier as we simply could leave the keys.
The area a is fantastic, lots of bars and restaurants and a really short walk into town, if you want to go there. The apartment itself provides everything you would like.

While we were 4 people sleeping was not a problem at all, while we were 5 we had to rely on the sofa. As that one is situated in the living from (windows to the street) this can be a bit noisy but as Sergio told us, the noise stops around 1 or 2 AM. And in a city like Madrid, where you probably do not want to go to bed before the early morning hours, we figured it does not really matter, anyway.

Taken together we had a fantastic stay and can highly recommend Sergios place.