We stayed in the one bedroom unit. Overall, we enjoyed our stay. Location is great in a quiet part of Shinjuku. It is within walking distance to the busy districts and Shinjuku station (15-20 mins walk). The closest station is Shinjuku-gyoemmae (7 min walk). There is a 7-Eleven around the corner and other multiple other convenience stores within a couple minutes walk as well.
The unit itself is very well kept and has a modern minimalist style to it. We were five people. Space wasn't really an issue. Note that even though it is the first floor unit, the floor itself is a few steps elevated from street level. So you will still need to carry your bags or stroller up a flight of stairs.
Having a little kitchenette and a washing machine with a dryer function was great. Heating comes from two units on either end and they provide coverage for most of the space. However, not the washroom so it can get quite cold, especially late at night and in early mornings.
We found check-in and check out very streamlined especially if you do the pre-registration online and have everything ready to go. When checking in simply enter your reservation code and then follow the instructions and video call using the provided iPad unit. Entry to the unit is done by door code so no need to carry a key or a card.
The only thing that would have been nice to have would have been more spots to hang things such as towels or jackets.
Would stay again!