That makes SWF slightly more attractive, though I'd hope that they expand their schedule given that the majority of people (both NI and US passengers) would be making use of the shuttle service because of the airport's remote location.
The schedule has 4 services daily - 220 seats each way - departing Stewart at 19:25, 19:45, 20:00, 21:00. The BFS flight arrives at 19:05, meaning people would likely miss the first and possibly the second shuttle, and there'll be a big problem if the flight is ever delayed arriving into Stewart.