I stayed in this apartment for a couple of weeks when I moved to town for work, and it was perfect! The location is great, and the apartment is super cozy and had everything I needed. Staying here feels like staying at a friend's place, it's charming and feels like a real home.
As others have noted, it's technically a studio but it's divided really nicely with a bookshelf into a one bedroom. The apartment is down a pretty steep and narrow set of stairs from the main entrance, but once I figured out the back entrance (no stairs) it was much easier to navigate in and out with suitcases. Laundry is in the building, but be aware that it is coin-op (there's an app that I couldn't get to work, but there's a bank nearby where you can get a roll of quarters). The apartment is ground floor on a side street, so there's the typical Harvard Square street noise (garbage trucks come by, college kids out doing their thing), but it felt perfectly safe. As others have said, the noise from the T kind of fades into the background and becomes soothing white noise after a while - I'm a very light sleeper and it didn't bother me at all.
Kris was incredibly helpful and super quick to respond to messages (like when I, completely jet-lagged and out of it the night I arrived, couldn't find the laundry area - it's directly across from the apartment). She's a great host, and I definitely recommend staying here!