A great place to stay! It's in the convenient neighbourhood of Hatagaya - two stations away from Shinjuku with lots of restaurants, small shops and convenience stores around. The people were very friendly there.
The apartment itself was small but perfect for two people. It was clean and there was a spacious closet to put suitcases and clothing. We were provided with bathing necessities and a hair dryer. As others have mentioned, the bathroom was tiny but it worked out fine.
Mitsuko was a fantastic host! She's very friendly and responded quickly to messages. Mitsuko was helpful and provided us with lots of maps and instructions as soon as we booked. After we checked in, my sister asked if the apartment had an iron and Mitsuko went back to her place to pick it up for us!
Overall, we had a great time and would definitely book the apartment again next time we're in Tokyo! I definitely recommend booking the apartment!