Great place to stay in Shinagawa. Shinagawa is not too busy but you can get ANYWHERE in Tokyo from Shinagawa. This apartment is not too far from Shinagawa station, I wouldn't recommend walking with luggage but is less than 1000 (10 usd) taxi ride from Shinagawa station. I would walk to Shinagawa station every morning and night because it wasn't too far and it's a nice enjoyable, safe walk. There's also Shimbaba station nearby that's less than a 5 minute walk, if you're not just using JR. This apartment is super accessible, clean, and in a great area. Would definitely stay again.
Note- I was by myself, this is a typical Japanese apartment (not very big) and I found it comfortable for 1 person. Don't know about more than that.