Martina’s place is great. It can perfectly fit 4 people or maybe 5 if kids,; very spacious, clean and with everything you need for a comfortable stay.
I met Martina, because I asked her if it was possible to leave out luggage a little before the check in, she is very nice, flexible and gave us a couple of tips to be aware of.
I loved specially the location, very easy to get around. The only inconvenient is the noise late at night from the street(bars and restaurants), I guess you get used to it if you live there, but if not, it can be a little hard to sleep.
Definitely I’ll stay again when I come back to Berlin. Highly recommended