We enjoyed our two night stay at Fernando's place : the apartment is perfect located and overall a good value for money.
Fernando is very welcoming and adapted breakfast to our dietary needs. He also provided us an useful metro/city map of Madrid.
A little downside : the window in the bedroom cannot be open, which means lack of fresh air after the first night. Also, expect many interactions with the host ; if you wish to be 100% independent during your stay, this might not be the best option for you.