We enjoyed our stay at Nena Apartments and the location in Kreuzberg was convenient for most of our activities and within walking distance to many restaurants, cafes and public transit. The room was as modern and clean as it looked in the pictures and is well equipped for a short (ie: 2-4 day) stay. We stayed for 2 weeks, so ran out of items like toilet paper, coffee pods and garbage bags, but the front desk was generally able to provide us with more supplies if/when we needed them.
On the negative side, the cooktop in our unit was not working, which I gather is a common issue in the units. The front desk agent was helpful in finding a new cooktop for us (the ability to cook some meals at home was our main reason for choosing Nena Apartments over a nearby hotel), but unfortunately the pan provided in the unit was not compatible with the induction cooktop, so we still could not use it. The wifi could be a bit spotty, and doesn't work down in the laundry room (there's also no signal down there). This can be a bit frustrating when doing laundry as the washer/dryer are managed through the WeWash app, so you have to run back upstairs to "reserve" the dryer on the app once the washer is done.
Overall we were generally happy with our stay, but would recommend for shorter trips than ours.