We lived in Eri's flat for two and a half months.
We are very happy with the flat. It is quite large by Tokyo standards and is in a nice neighbourhood without too much noise (apart from the New Year's Eve parades, perhaps). The train station is a ten-minute walk away and there are a few shopping centres, cafés and a large supermarket (Itoyokado) near the station.
Communication with Eri was easy and they responded very quickly. We had a problem with the washing machine and it was replaced the same day.
Overall, the flat is convenient, even for long stays.
The first impression after moving in, however, was mediocre, as the flat was not properly cleaned (dusty dishes, hair on the floor and in the fridge, sticky stains in the fridge). We had to clean the flat ourselves before we could settle in.
PS: Caution for those sensitive to cold: The flat can get quite cold in the winter months if the air conditioning is turned off (e.g. overnight).