One reason to change it was that the old pda looked like a palm pilot, and thus was asymmetrical in the left vs right hand. All other guns are symmetrical, so we changed it to make it have a gun-like handle, but still a flat screen facing the player.
Also, we use a clever approach for finding the muzzle position of a gun which didn't work with the pda. What I do is : when loading a weapon entity's mesh, I go through its vertices and find verts near the border of the bounding box on the muzzle side ( +Z ). Then I average these verts to give me the muzzle position. This works great for all of the guns we have so far, because it finds the business end ( which is square or round ), and gives me the center point of that structure. The scanner now has a spike sticking out of the screen that acts as the muzzle.
The scanner screen lights up when scanning something. Earlier, I was changing the gun's emissive color to make it more green, but that just made the whole gun greenish - not what I was looking for.
I decided to add a masked emissive term instead. The unused diffuse.alpha channel is now used for an emissive mask, specifying where the per-material emissive color shines through, irrespective of the lighting environment.
Right now the emissive color is used for the LCD screen of the pda, and parts of several weapons.