We stayed at Constantine's place between the 15th and 17th of December. The place is exactly as advertised, and kept very clean and warm. We didn't meet Constantine, but everything went so smoothly that we didn't need to. He keeps a cabinet of cleaning supplies that we made full use of to clean up after ourselves.
There are several shops on the main street if one gets hungry, including a fairly well-reviewed pizza/calzone/lasagna place, and a kabab house. Heads up for subcontinental and American guests, though: the restaurants here keep quite different hours from those back home. So the days we didn't eat at a restaurant, we simply picked up our meals from Stephansplatz, which is literally a ten minute's walk and five minute's metro ride away from the apartment.
The only trouble we had was finding this place when we first arrived, because our mobile data stopped working. It would be great if step-by-step directions were included in the confirmation email.