We are a family of 4 (two adults, one teenager, one child) and stayed at the unit for about a week.
The location is outstanding: Otsuka is a nice and quiet neighbourhood, with a convenience store right at the corner, restaurants and supermarkets nearby, and less than 10mn walk from the JR station.
The unit itself is clean and is equipped with everything you'll need, but it's tiny, even for Tokyo standard, no thanks to the two beds in the living area. If you don't need to access your luggages too frequently it's ok, but it's something to consider.
That being said we still very much enjoyed our stay.