One word review - recommended!
Key points - beds were comfortable, the showers were hot, the flat is spacious and was sparkling clean and the kitchen was fine for cooking dinner. And very importantly, the welcome was warm. (Thanks Dirk)
In more detail, the bedrooms and bathrooms are off of the main kitchen/dining area - so there isn't a living room. But there are TVs and armchairs in each bedroom, so in the minimal time we didn't spend exporing Berlin we would take all the chairs in one bedroom and relax there. The location is a short walk from public transport, and in the area there are lots of interesting bars and shops and restaurants - after 4 days we kept finding new interesting places - a real benefit of the flat. We all wanted to stay for longer.
Finally, if you want to cycle there is a shop which does rental about 50m away, relaxed staff and while the bikes weren't fancy they did seem well maintained.