We had a nice one night stay in Madrid but our experience at the apartment wasn't ideal.
There was first an issue with the interphone not working and then a party at the place next door as well as the normal noise of a Saturday night in one of the most lively areas of Madrid: the apartment is at a 1st floor and the good windows are not enough to cover it all.
The apartment is overall nice, with a lot of light and space, the kitchen is very well equipped.
The bathroom certainly could be renovated. Be careful with the shower as we had hot water for 10 minutes top and then had to wait a long time to get another 10 minutes...
The location is the greatest asset of the place: you are close to everything!
We didn't get to know the hosts but communication was good.