We enjoyed our stay here. Our two boys slept in the living room while we were in the bedroom. It was a comfortable stay even though it is a small apartment, which is expected in Japan.
Natsuko's apartment is very conveniently located. We walked to and from Ikebukuro station most of the time as it is a main station that has a direct Narita airport Express train - perfect for us.
There's also a handful of convenience stores, we bought heaps of bento boxes there for dinner. Who says you can't live moderately in Japan?!
We did our washing there too - Natsuko provided us washing powder and dried in the bathroom - no dryer.
You do need to keep your voices down as it is in a residential area as it is important to be respectful of the neighbours.
We recommend Natsuko's place. 4-5 people would be perfect! 6 or 7 will be rather tight, if you don't mind then go for it :)