http://www.thefirearmsforum.com/showthread.php?t=124587
That thing held on the trigger by the two allen-screws is a trigger shoe.
I don't understand your reference to "cam type device", or its helping with travel.
If you have a narrow trigger - let's say 1/8 inch wide, and your gun has a (for example) 6 pound trigger pull, then it FEELS like it takes X amount of force to pull the trigger. All the force required is being put on a strip of your finger 1/8" wide.
But if you put a wide trigger on your gun - let's says 1/4 inch, then the force required, while still being 6 pounds, will FEEL less, as all that force is not on a quarter inch wide strip of your finger.
A wider trigger FEELS like it reduces the pull. While many guns have different width triggers available, they have to be fitted to work well. It's much easier (and cheaper) to just bolt on a trigger shoe.
Or are you asking about this thing?
http://www.ezpulltriggerassist.com/