We stayed at Juan's place for a month. Juan and Juliana have been very responsive, reliable, friendly and kind hosts. Juan has been very flexible when I asked to adjust the dates of the stay, which I highly appreciated and Juliana was very flexible with regards to the timing of letting us into the flat. Juliana greeted us at the flat and explained everything to us. She was very friendly and helpful and I had no doubt that we could contact her anytime should we need anything or have any questions.
Given the situation with Covid, it was very good to see that the flat was super clean! Juliana explained to us that they put special measures into place to clean the flat. The flat is in a newly built building, nicely furnished, the bed is very comfortable and the kitchen is equipped with a little dishwasher, hob and an oven which was important for us as we stayed in the flat for a month. The location is great with regards to being in a very central part of Berlin, having Oderbergerstraße and Kastanienallee just behind the house where you can visit lots of great restaurants. The flat is close to several tram stops and it isn't far to the next underground.
The only downside of the flat, and that is something that Juan can't influence, is that all windows face the very busy Bernauer Straße, where there is lots of traffic, police, firefighters, and a tram going by and especially on the weekend there is additional noise from people partying in the Mauerpark or coming from Oderbergerstraße after a night out. While the windows are new they can't catch all the noise and so it is generally quite loud in the flat when the windows are closed and the noise when windows are open won't let you sleep if you are a light/normal sleeper.
Overall I would highly recommend Juan's place for a short trip when you are out and about the city a lot and want to sleep in an exciting area of Berlin, but less so for a long-term stay because of the noise level.