We stayed at Andreas's apartment for 4 days, it was perfectly convenient for our needs, in the smartest way.
It is fully renovated and it is completely new inside.
Also, it is very quiet - as it is facing the inner yard, and not the street - while it is also very bright, and has a beautiful design.
While the apartment is relatively small, it contains everything needed, in the kitchen and in the shower (despite their small sizes, they are very smartly equipped and practical).
Everything feels new and fresh - the bed linen, the blankets, the towels, the bathroom, the kitchen...
The location is excellent - just next to a metro station, with a supermarket and some restaurants nearby.
By metro, it takes about 10 minutes to reach Stephansplatz or about 5 minutes to reach MQ or Hofburg.
We travelled to Vienna by train from Westbahnhof, and it took us under 10 minutes on foot to reach the station (with luggage).
Andreas was fully available online whenever we needed to contact him, and our check-in went smooth with Marija who handed us the keys.

Tip #1: If the Internet stops working, unplug the router from electricity for a few minutes, and then plug again. Otherwise, it's super-fast and reliable.
Tip #2: There are two staircases in the building, each with its own floors and elevators - you need to take the left one.
Tip #3: The heating system makes funny (mild) noises from time to time, but we got used to it on the first day and it didn't bother us.

Very recommended!