This place perfectly met my requirememts. It was a new, modern, clean and we'll set up little serviced apartment. Seemed like good value too given the central location.
Location was very close to hauptbahnhof but of a small comment was that it is on the opposite side of the station from the S-line and U1 so its a little further than it seemed online. Easiest was to stay inside the station and walk through past the platforms 3-12 and exit the back door. From there it was only 100m or so... Great!
Otherwise not much to say, a we'll set up and run modern business style apartment. I did message the host asking about check in details and did not receive a reply. Didn't matter in the end but might have. For the record there is a staffed check-in desk till around midnight.
Only other thing is perhaps to note there is no air conditioning, normal for Vienna but some may expect it in a modern building. The weather was quite warm when I was there and the room was fine just with the window open.
I liked the place and would stay again.