We had great time in Berlin while staying 4 ppl at Axel's place.
Axel was very friendly and helping with suggestions.
Apartment was nicely warmed (we visited in winter) with a nice kitchen for catching up with your group.
Aesthetically is not great but it's practical and cozy - you can absorb aesthetics from the places you chose to visit in Town anyway :)
The place is literally 1 minute walk from U Bahn Stadtmitte and has all basics in foot-distance (market places, restaurants, bakeries etc.)
If you're interested in places like Kreuzberg, Neükolln or Friedrischain you'll still need 20'-30' rides but that's something completely normal for Berlin.
If you are a tourist in Berlin and you're looking for something central, this place will make your stay comfort and easy-going.