We spent a great week at Milena's place, which is pretty close from the centre (~15min by foot or 2 stops by metro). Overall the apartment is well designed with the full equipment that you can expect. If I had to find "bad" points for this apartment it would be that the shower has no door, and that you're actually seen by people that would stay on the bed (which wasn't a problem for us since we came as a couple but is quite important if you're not). Same thing with the toilets that has no lock on it but this is overall in the design concept of the apartment so it's not a big deal.
In the end I would say that it is a great place to visit Vienna as a couple, Milena is also really fast to answer and will help you the best she can if you need anything. I would recommend it.