I don’t think payment was ever that much of a holdup when it was required - as an SBS service you swiped your Metrocard at the streetwise ticket machines and then could board any door. It only held things up if the bus driver was “nice enough” to wait for someone fiddling with the machine.
That said, I assume the vast majority of pax use the service in conjunction with a subway transfer anyway but it’s definitely nice not to worry about having to get the ticket receipt right as the bus is about to pull away.
I’ve had issues with frequency in the past, as well as the location of the Terminal C stop, but they finally moved that somewhat closer to the terminal earlier this year, and service has been more regular for my last couple of trips.
They still need to adjust the timing on the traffic light right when the bus turns onto the on-ramp for the BQE. It *always* gets caught there.