Well, we just stayed here last week for 4 nights and it's a good place. 5mins slow walk to the subway exit. Safe neighborhood, the roads are well lighted and plenty of convenience stores around. Not to forget, there's matsuya and macdonalds just outside if u're hungry! Kazumi is a responsible host who made sure that we reached the apartment safely and easily. He will send the instructions days before your arrival! We used google maps to locate the apartment though. The apartment is as shown in the pictures and good enough to fit 2! Thank u Kazumi for the stay in your apartment!
Just a tip: it's easier to go by Airport > Nippori station > yoyogi station > nishishinjuku-gochome station. And vice versa. (Shinjuku main station can be very crowded and packed during peak hour which makes it hard to navigate with big luggages!)