We stayed at Stefans for 4 nights. The stay was very nice. Stefan was very friendly and helpful overall, and was there for us with any questions we had. Check in and out was uncomplicated and smooth, with only a short explanation session of the appliances.
Two things to look out for:
The airbnb is pretty central, so those with light sleep are better off with ear plugs, due to the traffic noise.
The other thing is that the apartment seems to have a bit of a moisture problem. Occasionally when we returned, the air inside had gotten quite humid. Although I think this is a general problem of the building, and not really something Stefan can fix.
Overall, our stay was great, and I can recommend staying with Stefan.