Highly recommended, It's the best experience I've ever had in airbnb so far! not to mention its reasonable price! The host and his family are so generous and kind, we had sushi dinner together at a local sushi bar and that was such a wonderful experience to discover Japan's transitional food culture.
There's something even better! Some IPA at local bar after dinner, and it was such a nice opportunity to have conversation with people in that neighborhood and meet the other side of Tokyo. Luckily enough, the host and I even had the chance to join their local shrine's annual festival on the next day, what a wonderful journey I had, even though I just stayed in Koiwa for one night.
I stayed in the traditional Japanese room, it's clean with super comfortable futon, tatami and great bedding. Way more comfortable than your expectation in traditional Japanese tatami room, I even ask the host where can I get the same set of futon and bedding.
There's a separated toilet on the same floor, I felt super convenient with it. The shower room is completely renovated, clean and modern. There is also a separated washing machine for guest and a beautiful balcony with good view for sunset and clothes drying, it's pretty handy for a backpacker like me.
By the way, the host said there are some hidden treasure inside the house, which is left by his grand father. Well, an indoor roller coaster is the only treasure I found and it was lit. However, rumor has it that people even met MJ and 2Pac in that house....interesting....