Just got back from a four night stay and have a great time. Unfortunately Marlen couldn’t meet us on check in but the instructions on where to get the keys was simple enough.
The apartment is in a great location and in easy walking distance of all the sights. The apartment itself is clean and has everything you need for a city break (may be cramped if four of you stayed there). The only flaw was the towels, which were old and had s slight musty smell first time they were used.
Overall we thoroughly enjoyed our stayed and would return if visiting Madrid again.