Perfect location! Traveling with kids we wanted something that is very central, but also close to the park and a little less touristy. I was on a conference trip so I walked to Atocha everyday and took the train while my family stayed behind and enjoyed all Madrid had to offer.
The apartment has 2 good size bedrooms each with an individual AC unit - an absolute necessity since Madrid had a heat wave when we visited at the end of may and we would have been miserable without AC. The 3rd room is very small and secluded with a single bed and no AC and we end up not using it much. The living area is very nice and also has AC. The kitchen is small but nicely furnished, and even had a Nespresso machine. As some has noted, the bathroom is a little small, and has a standing shower without a bathtub so it was hard to bathe the kids.
The apartment is on the 3rd floor, and the building has one elevator but it is very small (as everything is in Madrid!) There are also 2 sets of steps leading to the elevator, so if you have a stroller you will probably need to fold it - we had a double stroller for the two kids and we quickly realized that we cannot get it inside most of the places in Madrid anyways, so we just carried the kids when we went out to eat and took the stroller when we wanted to walk, especially in the park.
Communication with Fernando was easy, and the company that manages the apartment was also very helpful, they even offered to arrange transportation from the airport for a reasonable price but we did not use that option.
Over all, great place and highly recommended.