My adult daughter & I made this sweet little flat our home for 5 days (our second trip to Brooklyn/NYC). It's a short 5 min walk to the subway to get you into Manhattan - very convenient.
There is a decent size grocery store a couple of blocks away, however we enjoyed finding a Trader Joe's and shopping there - prices were a bit more reasonable we thought.
You will hear some noise from upstairs, but that is to be expected as there are small children and this is a wonderful old brownstone after all. I say some - it's really not bad. Expect it around 7/7:30 - it didn't bother us at all as we wanted to get up and get out and about, but you should consider this when making your plans.
The bedroom has a very firm memory foam mattress - comfy. The living room has a couch that can be made into a bed, however we didn't find the couch as comfortable to sleep on as we'd hoped. Jessica was great at answering our request for a comforter to add as a bit of a cushion and softening the area where the couch split.
The area is perfectly safe to wander around in. The look of the streets (a few blocks away from the apt) might seem sketchy and there are homeless people that might ask for change/food - they are harmless and hungry so we had no issue buying supper for a few - but we seriously felt very safe, often not getting back to the apartment until close to midnight. I only mention it so if you are planning to reserve this place, you won't be surprised or wary.
Jessica is very quick to respond to any queries you might have.