Me and my wife spent Xmas in Madrid and we stayed at Julio's apartment. What an experience! The apartment was great! Very well located, close to a bunch of interesting cafes, bars and restaurants. Also walking (very nice walk) to Plaza del Sol, metro stations and others. Julio was a great host and everything was very well setup and clean in the apartment. The internet was super fast, and it saved the day(s)!! Kitchen, bath and bed were in good condition. Absolutely no problems at all. The only "trick" here is the elevator is very small for all the people and luggage, but who cares?
Julio was very helpful and gave us very useful tips. Also, the apartment is full of magazines, guides and reference stuff for Madrid. Go for it!