The appartment has a nice location close to Okubo station which allows a very fast connection to Shinjuku station. The room I rented was located in the basement, which was uncomfortable to access with a big suitcase (stairs). The check-in was quick and easy, such was the check-out (leave key in designated place).
Before check-in, I had to fill in some forms which allowed to ease the check-in process which later is done digitally. After this process I got some documents describing the directions to the appartment, the check-in process, and transportation. It also had a small description about the house's facilities (airconditioner, IC) which I found very helpful as the controls on the devices are of course in Japanese.
I had the whole flat to myself, though I have to note that the walls to the neighbours are very thin. The kitchen has basic tools such as pots, dishes, and cutlery (no fridge) which is very nice to cook small dinners.
The bed is accessable using a steep ladder, so I would only recommend it to people who are not afraid of such.
All in all, nice small flat with its pros and cons depending on the tenant! :)