This was a great flat - very clean and tidy and quite a large space with 1 double and 1 single bedroom as well as a dining and living room. There's a patio too but we couldn't use it due to the rain. The flat is in a convenient location and a safe and quiet neighbourhood. It takes about 20-30 minutes by Metro to get to the main shopping belt (Gran Via). As some have mentioned, there is also a quaint little bakery nearby (Granier - just outside the Calle de Albarracín exit of the Metro, which incidentally is the closest entrance to the flat) with excellent cafe con leche, bread and pastries.
Staying in is also great - It has almost everything you need in the kitchen like pots and pans, stove, oven, dishwasher, herbs, oil etc. There was no kettle though but you can use a pot to boil water. If you want to cook, visit the neighbourhood grocery store on Calle de Alcalá where the locals go or else there are some large supermarkets less than 10 minutes away.
The washing machine was really handy before we went on the next leg of our trip. Wifi is good and there's a TV with a few English channels (Channel 15).
Willem was very friendly and helpful although we were unfortunately not able to meet him. He did leave clear instructions and guidance so we had no problem sorting things out. Overall a great experience and a lovely place to stay in Madrid.