First of all : this apartment is ok with the new Japanese law (problems are still happening in Japan because of that so...)
It takes about 10-15mns by walk to go to Osaki station (JR lines, including the Yamanote) + other convenient lines (you can go to Odaiba and Yokohama)
Shinagawa is at only one station so it is convenient if you need to use the shinkansen
The bus for the airport at Osaki station is at only 1.000¥ (the cheapest I have ever seen)
There is a Lawson next door, and also there is a supermarket close to Osaki station so you can buy good and cheap food (promotions every night at the supermarket) and also cook by yourself since the apartment is well furnished
Also, you can keep in mind that this apartment is spacious for a Japanese one, and the price is definitely not expensive (close to JR lines + wi-fi + pocket wi-fi)
I really need to add that Sayoko was the nicest airbnb host I ever had until now : we were able to check-in earlier, and drove us to the bus station with our luggages on the last day. She also lent me a thermometer and ice packs because I was sick, and went with me to the clinic and the pharmacy, so she really helped me when I needed it.