We stayed here for 4 nights, and very much enjoyed our experience overall.
Although it is much smaller in person than it appears in photos, it is undeniably high-tech -- there is a touchscreen panel to control windows sliding up/down/out/in, as well as rolls screens over the windows. They also have automatic rain sensors built in! Very cool.
However, because it's on the top floor of a sloped building, the ceilings slope down very sharply and steeply, meaning it gets rather bothersome for anybody who's a bit tall since you'll keep hitting your head. The stairs to the bigger bed above is an interesting experience; not too easy to navigate however, best enjoyed for the novelty of it. The biggest issue we had was actually the 3 very steep and narrow curving flights of stairs -- there is no elevator, and it was extremely difficult getting multiple heavy luggage up and down those stairs.
The apartment is very clean, quiet, and new, especially the bathroom and kitchen! The location is also top-notch, as the Neubau district is full of boutique shops and restaurants, and only 10 minutes away from city centre/Museumsquartier. Gerhard and Nicole are very accommodating and lovely hosts, excellent communication. Highly recommended (if you don't have heavy luggage and aren't too tall).