I spent 40 nights living in Tina's apartment and frankly speaking I am more than satisfied. Both Tina and Chris are very kind and responsive. In case of any issues they always respond very quickly. The apartment itself is tidy, it has everything you need. I think nobody will find any problems staying in it. Moreover, it's close to the metro station - Margaretengürtel, so you are in the center of Vienna within 5-10 mins.
I would stay with them again if there would be such a case.