The place is great, it's located about 4 km from the center (puerta del sol) which you can reach really easily (bus, subway or walk).
The balcony is amazing, it's on the 8th floor of the building (top floor) and has an impressive view of the area. The balcony has 2 sunbeds and gets a lot of light since it faces south.
The place has everything you need - the bed is comfortable, the bathroom is clean and the kitchen is well equipped. Internet is fast enough for browsing and I would say even for remote work.
Check-in is done via an app you install on your phone. Then, when you're there, you use the app to unlock the building and the apartment doors. The host is very nice and will walk you through the process, if needed.
All was great, I would recommend this apartment for a great stay in Madrid!