In short - the apartment was great, the location was less so (albeit well connected).
The apartment is small but comfortable. The bed is a good size and is very comfy, a small kitchen with a kettle, toaster, two cooker rings, and pots. The shower is fantastic, it is a rain shower with a separate head to rinse off with, and it is nice and big. The windows are partially frosted so that you can see out, but retain a feeling of privacy. I think the couch can turn into another bed, but it would be very small for more than two people. On the downside, the curtains didn't close fully, so the brightness of the city crept through during the night.
The wifi was good, but we used a VPN just to be sure as it seemed to be a public network. It was good enough to use Netflix at good quality.
The location has its upsides and downsides. The area itself is not the best, there are not many nice restaurants or cafés. On all of the nights that we stayed here, there were police cars racing up and down the road. It wasn't the most pleasant area to be in. The public transport is very close by, making it handy to get out to other areas to get to restaurants and tourist spots. This was really handy but also was loud. Due to the hot German summers, the apartment was very warm. However, if we opened the windows to cool down, we could hear the trains and the traffic (and the police cars) go by.
One of the things I love about Airbnb is that it feels more personal than checking into a hotel. However, I never met the host and only communicated through text, which felt a little impersonal. We found the check-in process difficult, as we only got the instructions an hour or two before we could enter the apartment. Each communication about the check-in was saying that we will receive the instructions within 48hrs, then that turned into the day of check-in, then just an hour before check-in. We found this awkward, as we were carrying out luggage around the city unsure of how we would get into our apartment.
Overall, the apartment was lovely, clean, and comfortable. The area wasn't the best but it was easy to get out of and around the city, and right into the airport. In short, the apartment was a good place to rest your head after a long day of exploring the city.