Full-Auto costs 2000 in Multiplayer. In the Campaign and Zombies, the attachment can also be used in conjunction with Dual Wield, which is impossible in multiplayer.

Its main downfall is that it reduces the CZ75's damage from 40-20, to 30-20, meaning it is much less effective than someone with a fast trigger finger (or Modded controller) in close quarters. 

Trivia

•  Full-Auto and Rapid Fire have the same Create-a-Class icon.
• This is one of five attachments exclusive to handguns, with the others being the Flashlight, Speed Reloader, Upgraded Iron Sights and Snub Nose.