We stayed there for a total of 8 nights from end May to early June. The reason for choosing the apartment in Feb was its location and its size (it's relatively large for Japanese standards). Our group comprised of 3 adults and 2 children (aged 4 and 6). Of course the sheer number of online reviews allowed me to make the choice effortlessly. After our stay, I truly understand why there were so many raving reviews! Here goes:
1) the host Koichi san is friendly and highly responsive via email and mobile. On our day of arrival, he offered to pick us up from the train station as we took the airport limo from haneda airport though we politely declined. However he still made the effort to drop by at night to say hi, teach us how to separate the waste etc.

2) the apartment is very clean
3) 4 single beds as shown from the pictures and one foldable mattress meant that it's good for small families or small groups
4) enough clean towels for 5 of us though we did the laundry a couple of times as we had a lot of clothes
5) convenience of having the launderette just 5 metres away from the block
6) very conveniently located near to shinjuku san-chime and shinjuku metro stations so it gave us easy access to various sightseeing places --- we did shibuya, harajuku, asakusa, tsukiji, ginza, akihabara, ueno, disneysea and even yokohama. It's near to kabuki cho but away from the glitzy night life. Very near to convenience stores so grabbing water, milk for the kids, or even onigiri (rice rolls) were made easy. If you like shopping at department stores, it's only 10 mins on foot to
Isetan or you could walk a farther for Lumine or Takashimaya.
7) throughout our stay the host made the effort to communicate with us to make sure that we were ok
8) on our day of departure he kindly sent us to the bus terminal though we had to check out before 7am
Highly recommended! Koichi san is a great host! Location is a plus factor. Price is good for family stay.