We (a couple) stayed at Kaen's place for 5 nights. It's located on a calm & quiet street, close to the main areas in Shinjuku (15 mins by foot) and well connected with public transport stations (2 train/metro stations, Okubo and Shin-Okubo are at 5/10 minutes by foot). The apartment itself is not large but I guess this is normal for Tokyo standards. It comes with a free portable wifi (limit of 3GB/3 days), for which we were very grateful. The bed and pillows were comfortable, we had good sleeps even having the AC on. Kaen is a nice host who responds promptly to messages, we didn't meet her in person but the communication was great. She was even nice enough to pick up a delivery for us. Recommended!