Had a great time at Yong’s place. As others have noted the stairs are a bit steep so it wouldn’t be great for people with mobility problems or difficulties lifting heavy bags but for us it was fine.
The location is great, Higashishinbashi-Koenji is a lovely little neighbourhood and Koenji is an easy walk away. The train from the nearest station takes you straight to Shinjuku so all of Tokyo is easily accessible. Highly recommended!