Area was very clean, and you can enjoy the convenience and feel of a small residential area within walking distance (10-15 min) from Shinagawa station. Staff were very accommodating and allowed us check in at 1130AM, which gave my travel companion and I the rest of the day to sightsee and wander around the area.
In terms of size, the room was exactly what you'd expect from a Japanese hotel. However, it included a small kitchenette and microwave. Very handy!
Being nearly 6ft tall, I found using the bathroom to be quite comical, as there is *very* little room in between the bidet and wall. The shower and bathroom amenities were your standard fare.
If you like soft pillows, comforters, and mattresses, then you will love their beds. I'd recently stayed a different hotel with a much harder bed, so this was like sleeping on a cloud.
The room included two small closets to the left, where you can store your belongings and hang up jackets.
Overall, I'm very pleased with my stay and intend to use Flex Stay again in the future.