I just got a Limb Driver for my Guardian and I really like it. I highly recommend it. If you don't want a fall away look at the Whisker Biscuit or Octane Hostage Pro.
The Trophy Taker is a proven fall away also - highly recommended.
You might consider starting with a Whisker Biscuit - becuase of its utter simplicity and ease of use. Then, you can decide to try a fall away later on if the mood strikes you.