Yumi's place is right next to Yotsuya-Sanchōme Station, which is awesome because it is an easy station to navigate and gets you pretty much every where else you need to go. It is also right next to a 24-hour 7-Eleven which is a great spot to grab a morning snack before you head out for the day (Japanese 7-Eleven's are the nicest and cleanest in the world).
The apartment is not ideal for super tall people, so be warned, but other than that it is great. You have your own washer and dryer, and an iron, which are key for me personally, and all the towels you will need during your stay.
There were a couple of times where my buddy and I could not figure out the appliances, and Yumi came out to help us very quickly, which was awesome. I felt bad that we needed her to come out twice. I would recommend that you have her show you how to operate the A/C unit, the washer/dryer, and the iron, especially if you are staying more than a day or two.
Overall, a great Airbnb experience. I would absolutely use this spot again.