I stayed in Rosa's place for a month and had a really good time overall. The size is good for 2 people although not very spacious. The kitchen is good enough to make most things, but cooking together can be difficult and there's no oven. The sofa bed and TV are very nice, but you do need to bring a laptop with an HDMI cable or similar to play anything.
The location is very nice too. It's close to various metros and to plenty of places where you can get drinks in the evening or when the sun is out. There's also a sport complex, a cinema and the national music auditorium within walking distance.
I spend 8 hours a day working from here during weekdays. I got my own chair because I did not want to sit on the chairs of the place for that long. Other then that I was able to work just fine from here. The wifi connection was also more than adequate (400mbit iirc).
I will definitely be booking this place again next time I visit Madrid.