The apartment is very clean and small (don't expect anything larger in central Tokyo). My boyfriend and I stayed for about a month and a half. It's super easy to get into with the keylock situation and very conveniently located to all major areas in central Tokyo. The Zens team is also great with responding right away re: any questions or problems.
I'm used to living in a big city so I thought the noise from the highway wouldn't be an issue, but it did take me a while to get used to the constant noise. The kitchen is very small and you could barely get any cooking done. Overall the apartment is great for travelers staying for a short time (a few days to a week), but maybe lacking some amenities and space for those staying a little longer like we did.