This apartment is fine. The location is great and the apartment's at the back of the building which means it's quiet. It's rather cramped, bland and characterless, but everything works and as a base for visiting Madrid it is functional.
The MIT House system is a bit annoying. The check-in system on the app didn't work, meaning multiple frustrating unsuccessful attempts to upload our passports. Also, the app based system for opening the apartment didn't work so we had to call the office. The cleaning was not finished until 30 minutes after check-in time.
MIT House is obviously big business - they told us they look after more than 200 properties in Madrid. They need to improve on some of these details.