I've set up my new Extra the same way as Wingspan has described, with the second elevator servo on channel 5 to minimize the delay between the two servos response time, and set it up on a switch. This was also on a 9C. I set it up with 50% travel, and even on 3D rates it wasn't enough to stop the airplane from rotating during a hover. I haven't tried them during a Harrier but I might do that next time I'm at the field. It might help give more control authority when the ailerons are less effective.