Staying at Andrea's appartment was super uncomplicated and was a perfect fit for our stay in Vienna. Since you can pick the key directly yourself at the appartment we were also independet regarding our arrival/check-in and communication with Andrea was very good and easy.
The appartment is located within less than 5 min walking to metro station Schönbrunn and therefore also close to the Schönbrunn castle. From there you can get to the city centre within 15 min to Karlsplatz/city centre.
The place itself is very clean and if you are two people (couple) it's just ideal. It's a one room appartment with a small separate kitchen, bathroom and toilet. The bathroom is quite small so a bit difficult to get ready in two in the morning, but that was not a problem at all for us. At night one can hear a little bit the traffic if you keep the windows open.
Overall this appartment is very good quality/price ratio.