We stayed at Arnaldo’s this September and had a good stay in Madrid. The apartment is a bit far from the centre (maybe 25-30 mins walk) but very close to the metro so it was easy to get around. It’s also extremely close to Retiro Park which was a nice outing.
The apartment is very clean. It was easy to check in with Airnaldo’s instructions. Our only issue was that we were only given one towel each for 5 days, and asked for more but never heard back. Otherwise had a good stay. It can be a bit loud sometimes at night, but we slept well with the windows closed and A/C on.