My friend and I enjoyed our stay in Airnaldo's apartment. It's clean, calm and modern in style. Check-in was simple with the help of the photos Airnaldo sent in advance. Location is great - just a short walk to the Retiro park and Reina Sofia, and not much further to the Prado, Plaza Mayor, restaurants, supermarkets etc. The beds were comfortable and the shower was great.
The windows all look out onto a small courtyard, which isn't very exciting but I guess means there is no street noise to worry about.
There is no kettle, which coming from the UK, we missed. But this seems to be normal in Madrid airbnbs, and my friend still managed to cook us a huge breakfast using the stove, pan and other implements provided (there is a stove-top coffee pot but we didn't use it).
The toilet/shower-room is adjacent to the kitchen and has an opaque glass sliding door with a 'cut-out' door knob - very stylish but not exactly soundproof - so it helps if you're fairly comfortable with the person you're staying with!