Staying at Singer109 was a great choice in my first time in Berlin.
I wanted a more relaxing place, and I got it. The staff is kind and helpful, the facilities are well preserved, clean and everything works properly (including the kitchen).
There is a big lobby for guests to chill and/or interact if wanted. I was lucky that the other guests, surely younger than me, were very respectful, polite, and quiet.
The 5€ breakfast is a plus, since there are no bakeries, coffee shops or restaurants immediately around.
If you dont mind staying in a room with some other 3 or 5 people, the cost benefit is positive.