I'm not totally sure I would stay in this flat again.
On the one hand, the location is GREAT. The Friedrichshain neighborhood is absolutely wonderful, and most of Berlin's attractions are about 30 minutes away by transit (there are lots of stops nearby). It's wonderful to have a washing machine/dryer in the apartment.
On the other hand, the neighborhood is very, very noisy—Boxhagener Strasse is a main road, and cars drive down it all through the night. If you're a sensitive sleeper, you may have trouble in this flat. Additionally, the bedding was quite poor in my opinion. The pillows were very lumpy and uncomfortable, and the beds had no sheets.
Lastly, I have concerns about the difficulty of contacting ElPilar. Multiple times while we stayed here, people staying at other flats in the complex stopped me and my friends to ask for our help checking in. Their codes to their flats or the lockbox didn't work, and they got no answer from calling ElPilar. This didn't happen to us, but I worry that it might. I think this is a big problem that ElPilar has to fix.