We stayed in this apartment for two weeks and we loved it. Location is great, in a nice little street close to the main road of Okubo (Korea Town). Shinjuku station was a 15 minute walk and Okubo station a 5 minute walk.
Kaen was really nice and gave us a lot of suggestions for restaurants and activities. On rainy days we could grab an umbrella from under the stairs. She was also really quick to respond.
The apartment itself was small, but perfect for two persons. The bed was comfy and the air-conditioning was great. We needed it.