I'll start with the good parts: this apartment is located wonderfully, in the heart of Malasaña, one of my favorite parts of Madrid, near all sorts of fun bars and restaurants and shops, yet tucked away enough that it's quiet. And the check-in process was smooth and simple, and the apartment clean and decently maintained. It's not particularly big and nor does it feel very luxurious, but it's comfortable enough for one person and has most of the things you might need over the course of a short stay.
I did, however, have a quite unpleasant issue with the door - it's an old door and the wood literally swelled so much in the humidity that it became absolutely wedged in place and unable to open, which means that I had to spend my last morning in Madrid waiting for the superintendent to fix the door (which took quite some time). To his credit David was a fast communicator and gave me a partial refund, which I appreciated and which was in line with the general good communication throughout my stay, but it was nonetheless an unpleasant experience and one that would make me think twice before staying at this apartment again - no matter how good the location may be.