Excellent long term stay! We spent a month there, it has everything you need, very well equipped, heating for the winter, very fast internet plus an extra room with a desktop in case you need to work. The bedroom has an amazing bed, very comfortable. It’s located in a very quiet street but also very close from all the activity of Malasaña and less than 30min by foot to all the things to visit in Madrid. The only drawback I see are that it’s not very luminous and that it’s located at the fourth floored the no elevator so it might not be accessible to everyone.
I would recommend 100% to stay there, everything went so well that we only needed to write to them at check in and check out.