We stayed in the flat for five days. The location was not central but very near to the U-Bahn 5 (one of the most important ones for tourists I'd say). The flat is very nice and big and especially the couch is heaven after a long day of walking through Berlin! As you probably saw in other comments, the door situation is a bit weird, you should be a family or close friend group if you want to stay here as there are no doors between the different sleeping areas. The kitchen wear should be updated, as for example the pans are so scratched that you couldnt really use them.
The communication with Michael was great and the check in and out worked perfectly!
Thanks for the nice vacation, we would definitely stay at Michael's flat again!