This flat is in a great spot in barrio de Salamanca - an area I always stay in. Not too far from the tube (line 5) and plenty of restaurants / bars etc within easy reach. if you like walking, it's about a 30 min walk to the centre.
The flat is fine but a bit functional. it was fine for me as I was out and about exploring for the weekend but if I'd wanted to be there for longer or to spend more time chilling there it wasn't really cosy or homely.
it was clean though, bed was very comfortable and there was always hot water for the shower. Kitchen has everything you'd need for some basic cooking.
Enjoy your trip to Madrid!