The Custom X is a directional camber board, the Antler is closer to a twin with a flying-V wet noodle profile. I don't get how they're similar?
I don't know why they get compared so much, but I assumed it's because the technology on the Antler is Burton's fancy stuff. It's one of the their high-end boards. I don't think anyone's saying it's going to ride like the X, but it's light almost like the X. At least, I don't see how it could ride anything like the X.
On their website I think they say it's between the Joystick and the X.