My partner and I stayed at James' place for almost two months right after moving to Berlin. In our experience, here were some of the pros and cons of this apartment in terms of a long stay that included one of us working from home:
PROS
(1) Fantastic natural lighting!
(2) Great location, very close to Tempelhof Field, where we absolutely loved to go biking.
(3) We needed an Anmeldung and even though we had forgotten to discuss this with James ahead of time, he was able to quickly help us out with the documentation.
CONS
(1) The apartment is too small for two people, and not well suited for working from home (there isn't a good desk and chair set up for working, and internet connection was a bit spotty). We got a bit unlucky that there was a demolition project happening in the backyard that this first floor apartment faces during most of our stay, and so that also made working from home challenging.
(2) On the minor side - there is no towel drying rack in the bathroom.
All in all, this is a great spot if you're on vacation in Berlin and are looking for a place to come back to at the end of the night. Lots of cool bars and events happening in the neighborhood. Nice for a long stay too if you're just one person and have a co-working or office space from where to work. Photos of the apartment shared on the Airbnb page are quite accurate; only thing to keep in mind is that the apartment does not look as new and pristine as in the photos.