Myself and my boyfriend are just back from a great stay at this central apartment. It was very clean - towels, toilet roll, irons, hairdryers, washing tablets etc were all provided on arrival.
The location is great - it is right in the centre of all the restaurants and bars, which is a very noisy/busy area when outside, however in the apartment we could not hear a thing. We were 4 mins from the train station Sol, which can get you to lots of different places (in Madrid city centre and also the airport).
The check in was very easy - Katherine was very friendly and willing to help if we needed anything.
The kitchen is fully equipped with everything you need to cook. It was perfect for a short period of time - e.g. making breakfasts etc.
Only slight negative of the apartment would be that it is advertised as having a balcony. It does have a small balcony, however half of it was covered with two fixed generators - meaning that you can only really have one person standing on it.
It was a great trip and I thoroughly recommend booking this apartment if you are in Madrid!