I should begin with the apartment. Until now I Stayed in 3 different zones in Madrid, this one was the best for sure. Near Retiro park, you can just walk without using the metro to get to any location.
The building is very beautiful, the room is kinda small, with a big and modern private bathroom (it's a big plus).
Now about the Host and Check-in Process :
I have some communications problems with the host, he doesn't speak English at all. On Airbnb, he sent me replies in Spanish and I auto-translated them.
The Check-in Hour its 3 PM, I'm using Airbnb regularly and I always "negotiate" the check-in hour if, but for this host was not the case. I arrived at the apartment at 2:45 and I ring the bell, call him, and didn't respond.He send me a message in Spanish after 10 minutes saying that : Call again at 3PM .
So that's it, the apartment and zone is worth the money but you can have some stress on the check-in process.