I've used it before and it didn't do jack except put a pretty red thing on the screen. Waste of a perk slot(s) if you ask me.
You can basically equate its effect to headshot multipliers anywhere on the body. Drift0r did an excellent video explaining it, and thus is where I have much of my knowledge from. Here's the video: Ghosts In Depth - Deadeye Perk Review (Damage & Probability) - YouTube. Also, look in the description. The first link is his source, which put together some excellent charts and graphs to show how different damages will be affected (in % of 1 less shot to kill...cuz that's pretty much all it can do). I'm not sure..and not sure it says anywhere..if these multipliers stack on top of existing headshot multipliers (when applicable) or not.
So, keep in mind that the gun and range (as well as maybe any existing body multipliers), which all affect the base damage dealt, play a factor on whether it can help you or not. Have a look-see, and then you (and anybody else) can decide for themselves.
Personally, I'd say either Specialist or Gambler are the only ways I'd roll with it.