Yasu's apartment is an excellent place to stay in Tokyo. It is about 10 minutes walk from Takodanababa station in a very nice area, and there are a lot of great food options around. If you want to you can actually walk to Shinjuku (it takes about 30 mins) which is a great way to stretch your legs and save on a train/taxi fare.
The apartment itself is very cool - the rooftop area is a great place to relax and the apartment has a nice layout with the loft area and central staircase leading downstairs.
There are only a couple of drawbacks: the area itself can be a little noisy due to the road outside, and there is also a restaurant downstairs which can be noisy and means the apartment has a certain restaurant-smell to it. However it was quiet during the nights - the traffic really drops off and the restaurant shuts around 10 - so this didn't impact the experience much at all.
Overall I loved my time at Yasu's place and I would definitely stay there again. I would recommend this place to anyone looking for a base to explore Tokyo.