The actual location of the apartment was not at the location in the reservation confirmation. The actual location wasn't revealed until I got a message from the host who said that directions would be provided the day before check-in. However, that email did not provide instructions on how to reach the apartment. The actual entrance was on the side of the building, not visible from the front. As a result, I could not get the key and had to leave my suitcase at the apartment street entrance so I could look for a public phone to contact the host (thank goodness Japan is so safe!). Although the host said they would only respond to requests between 10am and 6 pm, I was able to speak with someone who met me at the apartment.
After getting the key (this was well past 7 pm) I had to climb a steep narrow staircase with a heavy suitcase to get to the apartment. The apartment was basically clean, but I gradually discovered many items in need of repair, such as the curtains, light stand (I fixed), sink/stove area, ceiling lamp, TV (no remote control), and router (no internet signal). The last was of particular concern because the ad implied that pocket wifi would be provided so I had not rented a cell phone. I ended up going to Shinjuku Station where I could get free wifi and ordered my own pocket wifi from a company in Kanda which allowed me to pickup the unit the next morning. I also sent an email to the host requesting internet service and a TV remote, but didn't receive a reply until 2 days later.
The host fixed the router a few days later, eventually provided a TV remote, and agreed to refund me half of the cost of the pocket wifi I had rented. I actually got the TV to work by downloading a manual, using the side buttons on the TV, and connecting a UHF antenna I found in the apartment because there was apparently no signal on the TV cable.
From then on my stay was uneventful, as it should have been from the start! The kitchen was well-stocked with most of the things you might need, the floor and walls were pretty clean, and all the appliances worked once I figured out how to use them (I can read Japanese, but non-readers might have difficulty). It was a quiet location only about 3 minutes from either Shin Okubo or Okubo Station, and there was a small grocery store right on the main street there (My Basket).
The Okubo neighborhood is not a typical Japanese neighborhood as there are a large number of non-Japanese residents and stores. However, since I did not spend a lot of time in that area, that was not important to me, and it felt as safe as any other neighborhood in Tokyo.