If you're looking for a comfortable, convenient and budget-friendly place to stay at during your time in Tokyo, this is the place.
The apartment itself is situated around 5 minutes walk from Higashi Shinjuku station, although depending on your travels, you may find yourself walking 10-15 minutes to/from Shin-Okubo station instead - but the walk is pleasant, and you get to see the residential aspects of the city if you take the back streets.
The area where this apartment is situated is great - multiple convenience stores nearby, and a diverse variety of foods, including hand-made soba, udon, burgers, cafes, Korean snacks, and even a 24-hour seafood BBQ place downstairs.
Check-in procedures are low friction.
If you're a light packer like me, and you're in the city for a few days (or longer), the supplied washer (with spin dry) is invaluable. The bathroom/shower was also a favourite of mine, allowing you a lot of flexibility into how you want to shower, while the air extractor in the shower proved really useful for quickly drying those damp clothes out of the washer.
Overall this is a highly recommended place to stay at.