There are a lot of different options out there in guns to use in martial arts training, including wood, plastic, rubber, and with various degrees of realism.
I know from working with knives that the differences in material and behavior makes a huge difference in training. A rubber knife simply doesn't behave the same as a wooden tanto, which is a different weapon in behavior from a metal training knife. Not just in terms of effectiveness or realism, but in terms of what you are actually teaching.
Given the rather dizzying array of options when it comes to training guns, what are the advantages/disadvantages of different styles of weapon (and different styles of mock) and different materials for use in drills?