We stayed at Marco's for 2 nights and booked for 3 people. Cause of an emergency we only came with 2 and Marco instantly changed the booking without us asking for it.
The room was perfect! Located super close to Schloss Belvedere and two tram-stations.
Marco itself was super friendly and explained us everything we needed to know about the surrounding and Vienna itself and gave us maps and guides.
We would definitely stay there another time.
We can definitely recommend it!