My wife and I stayed at Sergio's apartment for 5 nights in late April right at the start of our Spanish holiday. Sergio provided great instructions to easliy get there from the airport by Metro and had set up easy access to the flat with the building porter who was waiting for us. In the first coouple of days we had a few questions for Sergio and he was very responsive and helpful.

The aprtment is so nicely decorated it looks like someone just moved out and left plenty of space for the tenants, and it is nice and homey with a good big screen TV and all the amenities you need. It is also a very quiet apartment, which helped to get over our jetlag, and the bed is super confortable.
The other thing we really liked were that it was in a non-touristy area, so the location gave us more of a truly Madrid experience with small shops bars etc. but still very easy to access the attractions of Madrid by foot or Metro. There is a Mercado just down the street, and be sure to try the Jamon Iberico de Bellota. Super! Also Sergio recommended some restaurants close by. One is El Estay which we loved. Check it out. Great food , great wine and nice people. We highly recommend this apartment!