I like to separate my review into categories so here goes

A) About the apartment
1) The location is very convenient. Just 200 meters from the Higashi-Shinjuku subway station.
2) The rooms are reasonably sized and good enough for 2-3 people.
3) There are some excellent places to eat in a 200 meters radius like an amazing sushi place, very good curry soup joint (a Hokkaido speciality) and a very good japanese style barbecue place.

B) About the host (Ming)
1) Very nice and helpful
2) Tries to accommodate requests
3) He gave us a special discount as my friend was leaving early and so that I don't have to pay for the entire room for 1 day
4) The room we got initially was quite small for 2 people and so he shifted us to another room as soon as it was available
5) He will also be happy to take you around and tries to keep guests informed about events around the area.

Things to be careful about
1) Tokyo is very hot. Try to make sure that during summers you do NOT get a room on the top floor (pent house)
2) The things that upset me most was the inadequate number of bathrooms and toilets. There was just 1 bathroom between 9+ people and 2 toilets.
3) Because of the high number of people using these spaces sometimes they are not clean (especially the bathroom)

Overall the place is good if you are on a tight budget. The location is very convenient.
I give this place 3.8 stars (I had to give 4)