We got the key from a person who waited outside the building (you need an Internet connection to communicate using WhatsApp), he didn't know a word in English but it was fine because everything in the flat was in top shape. Modern, Clean, well equipped, and extremely quiet (no sounds from the neighbors through the walls or from the street).
The flat was warm (in May) even though there was no heating on, I figure that in summer it's a minus and not a plus.
The "Balcony" is just an enclosed area in some kind of technical area of the building, it's not facing any street, only walls.
Internet was fast (Tested 35Mbit) and quite sufficient for our needs. Plenty of towels to go around and great water pressure in the shower.
Oh, and needless to say, the location just can't be better, it just can't. You are right in the middle of everything and public transportation in Vienna is great.
All in all, it's a wonderful small flat. Maybe only for the summer months, I would try and look for a place with air conditioning.