We had a lovely stay over the New Year period. The flat is centrally located, and compact but stylish, with everything you'd need for a comfortable stay.
As others have mentioned, light sleepers may struggle. The trains didn't bother us, but the bedroom is close to the front door - and sound echoes easily since it's a narrow stairwell. (The entrance is not recommended for anyone with mobility issues or heavy luggage!)
As is common in Japan, there's no central heating, but the electric heaters and traditional tub kept us warm enough.
Overall we enjoyed our stay and would go there again.