I stayed with Christa and Zach for a bit more than a week while on a trip to NYC. The house is nice, spacey and the two of them are super flexible and greatly experienced hosts.
Flatbush has a nice neighbourhood vibe to it and one can definitely feel very "at home" here. The room I had is tiny but they are totally upfront about that in the description and I didn't mind at all. Who wants to stay in when in NYC for a limited time anyway, right?! But yeah, for more than one person it might be less ideal.
A few things to keep in mind. I shared the house with C&Z and temporarily with other guests, too. While they try to manage and coordinate nicely, that still can mean 5 people for one bathroom in the morning. I guess when on vacation that is no problem at all though. NYC is vast and the 2/5 metro isn't that far from the house. However, make sure that suit your needs or u might end end up spending lots of time on the public transport.
In general I can recommend staying with C&Z.