Let's get some facts out:
Fly holder will accept only Fly steel. The center of the holder (steel channel) is skinner than the front and back, kinda like this )(
Fly steel will work with Fly or Edge holder.
Edge steel cannot fit into Fly holder.
Fly holder is stiffer in the front and softer in the heel to allow for more ice contact when coming out of turns. Same idea why they softened the rear outsole on the Hyperlite boot. Overall, it's significantly stiffer than the current EDGE holder. You cannot twist the Fly holder with your hands like you are able to do with the EDGE holder.
Same height, same dimensions, some bolting pattern.
The trigger is grey, like the current EDGE holder.
Weight is the same as the EDGE holder.