I spent a month and a half in Katherine's and François' studio. From the point of view of somebody who knows New York (I lived in New York for 13 years in the past), these are some of the things that I think make the studio fabulous, and which are not that easy to find in comparable small New York apartments:
(1) Spacious (for NYC studio standards), filled with natural light, great ventilation (2 windows and a bathroom skylight), a separate, functioning, and well stocked kitchen; everything is clean, no pests of any kind.
(2) Your own washing machine (virtually impossible to find in small NYC apartments), and a shared dryer just outside your door.
(3) Very quiet, no neighbors above, and nothing that can be heard from anywhere else. Just a little bit of totally normal street noise from time to time (way below the average street noise for NYC). I slept perfectly every single night.
(4) Excellent heat, and a modern A/C unit which also can be used to heat up the apartment in the winter if you are up late, when the regular heat is less intense.
South Park Slope is a great neighborhood. Everything you may need is walking distance. Interesting coffee shops not far away (Roots, OS, Colson). Downtown Manhattan is only 20/30 minutes away on the subway. Several Citibike stations nearby. And a totally safe area if coming back late at night.
I didn't meet Katherine or François in person (they were away during my entire stay), but any time I contacted them I received almost immediate responses. All the communications with them were clear. Check-in and check-out were easy. I would absolutely stay again.