Very nice flat, in a basically abandoned building (Feb 2023, I'm guessing big building works pending, most of the other flats currently empty), meaning very quiet and no neighbour to disturb ;)
I liked the location: next to an entrance to the beautiful Augarten park, pretty central and well-connected with Praterstern station (one of the hubs), ~10mn by tram.
A small drawback: 4th floor without elevator
The kitchen is fully equipped, with even salt-pepper-oil, and a big fridge&freezer. Markus is also supplying drinks and coffees at fair prices.
The wifi was good, not outstanding but fast enough (10-20 Mbps), and my only problem was that neither from the table nor from the couch could I plug my laptop (the table was probably too cumbersome to move, but the couch and coffee table I probably could have if really needed)
The bedroom was comfy and well arranged :)
In overall I had a very good stay at Markus' flat !