Fernando is extremely enthusiastic host. He is able to provide a lot of useful information which helps you to save a lot of money (e.g. tips for nice places, views or restaurants). His place is very well situated, being in walking distance of the city center as well as the riverside.
During our stay, Fernando kept supplying us with a bottles of mineral water and prepared some typical Spanish breakfasts for us. We also got a lots of small gifts.
In overall we've really enjoyed our stay in Madrid and Fernando's flat was a great base for our exploration.

Only downside I can think of is that people who are not accustomed to such enthusiasm/interest may feel a little bit uncomfortable at the beginning.