These knives have started to ship.
Regarding the differences in "feel," I should probably start by saying that Zytel is a great material for durability and reducing weight, I personally have focused my knife buying attention (and affection) on other materials (such as G-10, aluminum, carbon fiber, titanium, stainless steel, wood, etc.). There is nothing wrong with the Zytel handled Flashes whatsoever! I just like the aluminum Flashes more!
The aluminum Flash has a bit more weight; and for me, it gives a more solid feel in the hand. The Zytel Flash II weighs 3.1oz and the aluminum Flash II weighs 4.3oz (my unofficial measurements on one of our higher-tech postal scales). The opening mechanisms are the same, but when the knife clicks open, theres just a different feel and sound of steel-on-aluminum versus steel-on-Zytel. Ooooo!...is all I can say. And tactilely, theres just a different feel of cool, smooth aluminum.
Most of it Ill say are just aesthetics. But for me, they are very important areas!