Sebastian is a lovely host, very energetic and welcoming. The flat is very conveniently located for walking around to shops, nightlife, and cafes and I had no problems getting in and out. In terms of value and convenience, I'd rate my stay highly.
A couple notes: you may end up sharing the bathroom with another Airbnb guest in the room next door to yours, and you may be able to hear noise as they come and go. A good set of earplugs will avoid any sleep interruptions caused by this proximity (you can individually lock your room).
Speaking of earplugs, there seemed to be a lot of street and construction noise that leaked into the room during my stay. It's in the city, so that's not unusual, but something to consider if you're sensitive to sound.
And speaking of sensitivities, if you don't like the smell of 🚬, you may be put off by the occasional smell that lingers up from the lower floor. Even with the door closed to the downstairs, a slight odor would find its way up to the hallway leading to the bedroom from time to time.
Generally these were minor issues and didn't erode the overall experience of my stay. YMMV.