Melvin was a wonderful host — he stored our bags for very cheap on the first and last days of the trip (before check-in and after check-out), and offered to get us a cab from the airport. Whenever we had questions he replied very quickly and sent someone to the apartment from his office to help within minutes, if necessary. The apartment was very clean when we showed up and had most things you would need in a kitchen (not all, but most). There was one bath towel per person, which worked for us. The location in Madrid was definitely the best part — we were within walking distance to most of the locations we visited during our trip, and felt pretty safe walking around at night.
My main complaints would be that during the beginning of the trip, the door lock was not secured properly and almost came off when trying to lock the door, the power went out, and we only had one set of keys for four people when we should have had two. Melvin sent people very quickly to fix these issues for us, but it was still a slight disruption to our trip every time we had to report a problem which we needed help with. The apartment is also much tinier than the pictures make it seem on the website, but we still made it work with four people.
Overall, the apartment is a great value for how cheap it is — we didn't have any major issues and it was a great place to crash. Thank you Melvin for a wonderful trip!