There are several advantages to the LCY service to JFK as far as I am concerned. The advantage of clearing customs of course, plus the benefit of being able to send and receive emails for most of the journey. It has to be the best BA Club service.
From experience the crews are exceptional being in a league of their own including many of the flight deck who are genuinely passionate about the service.
I have used the service in both directions on a great many occasions and when the loads have been low was told it only needed 11 people outbound to break even! I must admit I am not totally sure how true that is?
It would be a great shame if the service was to discontinue although I usually catch the first flight because of connecting in New York.