We used it last summer. We live about 30 minutes away from Gatwick, and for us it worked really well. There was no one in the queue (we arrived about 8.00pm) and we were allocated the seats that we wanted. The following day meant we were under less pressure to get to Gatwick very early to beat the queues and ensure we got seated together.
Has Twilight checkin started up again? It was cancelled after 11 September, and I hadn't noticed that it was available again.
Regards
Rob