We enjoyed the stay. This place is one of few in Madrid for reasonable price that allows you - if you are not traveling as a couple - to have proper beds in separate rooms. The transport connection is also fine, even though not directly in the busy downtown. The communication with the host (and his contact person) was impeccable - available anytime via messenger, just perfect.
The only problem we had was the heating as it was a very cold week in Madrid (around 0 degrees) and the apartments are not made for proper heating. We managed to heat up a bit with electrical heaters and air conditioning (the host also immediately provided a small additional heater device). Take warm clothes for home :-)