We had a great time in Asagaya at Kimmy and Dee's place. The location almost couldn't be better. Very easy to find, quick access to the city center and other popular destinations. We actually used the Marunouchi subway line more often than the Chuo line because you can buy a subway day pass for just 600 yen. From the apartment, you can also easily get to Saginomiya and hop on the Seibu Shinjuku Line to get to Kawagoe, for example. However, you can already spend a couple of days exploring just Asagaya and Koenji.
As for the apartment: It has all the basics, so if you're not planning to spend a lot of time indoors, it's absolutely fine, and the portable wifi is extremely useful, especially if you don't know your way around Tokyo, but keep in mind that it is very small. We were 4 people and there was barely any space left to put our luggage or hang any clothes. So, if you're booking for 4, make sure you are of the frugal kind and very comfortable with each other, otherwise I would recommend booking two apartments.
Lastly, we did have a couple of unfortunate instances of cockroaches entering the apartment. I don't fault the host or the owner for this, since the apartment was clean enough and they are very common in suburban Tokyo and many houses are rather old, so they'll find a way in one way or another. Kimmy and Dee were very quick to respond to it and sent someone to lay out some traps.
In conclusion, I wouldn't hesitate to book with Kimmy and Dee again. We felt taken care of and we did have everything we needed to tackle the big city.
Thanks again.