My boyfriend and me stayed five nights at Petar's place. Even if we arrive late at night, there was no problem at all to check-in; and the same to check-out, Petar was really flexible.
The place is really cozy and welcoming, we had a great time. There is a tram station just one block from the building and you can move easily around.
The communication with Petar was really active and he always answer fast.
We recommend this place if you want to spend a long weekend in Vienna in a residential area well-connected with the city center.