Had a great experience. The location was very close to public transportation and in a great part of Shinjuku. Pocket wifi was nice and Ichimaru-san was very responsive and helpful. Convenience stores are right around the corner should you need a quick run for anything and there's a vending machine right next to the apartment should you need emergency coffee.
There's a water heater with only about 1 hour of hot water per day but that was never an issue for 4 people. The bathroom was quite small and the apartment, while quite spacious, can probably fit 4 people comfortably. 6 only if you're bringing small children.
Aside from that, the place was great! Highly recommended.