The most important thing to mention is that this place is SMALL. For two people, it is perfect. For more than two it gets very cramped. It's definitely do-able, but do be advised!
The location is awesome. Literally a 5 minute walk from Shinjuku Station and some incredible sights, food, and shopping. Very easy to get around and the directions (with pictures) to get to the apartment are detailed and helpful! The apartment DOES have A/C which is a must in the summer, and the temperature was great once we got it running. The toilet and shower/bath are excellent and functioned perfectly. We didn't use the kitchen, but it would suffice for a quick meal! The living space was cozy and would be most comfortable for two people who could use the futon as a couch instead of a bed.
Checking in and getting into the apartment was a breeze, and we felt very safe the entire time! We were three young girls traveling alone, and this area of town is safe and clean as far as we could tell. No issues whatsoever. I highly recommending this place for a first visit to Shinjuku-- if I go back, I'd love to stay again!