I stayed in Martin's flat for 7 weeks over the summer and it was a good place to stay overall. Good value compared to other places I saw, and a decent amount of space for one person staying there. The kitchen was generally well equipped, although I never actually used the mini oven. The air-conditioning downstairs worked really well which was super important in July and August, the only thing was that I found it unbearably hot trying to sleep upstairs and resorted to buying an airbed so I could sleep downstairs (but even with that cost I think it was good value). There were plenty of towels and bedding, some lovely views, and communication with Martin was really good. It was also close to the metro and surprisingly quiet.
The area is probably not for everyone. I really liked it, it's very diverse, there were loads of bars and restaurants nearby and I loved San Fernando market just round the corner. It is probably a bit poorer than other central areas of Madrid and although I never really felt unsafe I did get pick-pocketed late at night when walking home. So just be aware of your surroundings and keep your hands in your pockets!