Just the right size for a group of 4! I stayed here with three friends, two slept in the same full/queen size bed, one in a double, and one on a comfy futon on the floor. We still had plenty of room for our suitcases (each of us had a large carry-on sized suitcase). Hatagaya is a really cute neighborhood, and very close to Shinjuku.
Masami-san's apartment is one of the few AirBnbs I've stayed in Tokyo where it actually felt like a comfortable living space. By Tokyo standards, it's pretty spacious, so it's a fun chance to imagine you're living in Tokyo here, even if it's only for a couple days.