you set one unit the highest priority to cc.
Whenever it is possible to cc that target, it trys it.
its basically the same like mouseover fear, except that it checks for allready applied ccs and dr timer + LoS/range check ect.
for the use of our modifiers it made much more sense having one modifier to set a specific unit to cc then having a modifier that only casts a mouseover fear, which simple could be done by a macro (in combination with the pause button)
In my view it has much more pro's then con's
it has a 100% accuracy because every unit has an unique ID
it only cc's non dr'ed units with predefined checks
you can choose what to fear without holding down the modifier button all day long

( especially in 2's (I play my lock with a boomy) first I allways choose to cc the dps if we fight against dps+heal, even if we stick on the dps. After we made enough pressure I switch my primary target to the healer.)
Another good thing is! It implements itself flawlessly into the rotation.
You could also use it in Raids where you have to fear a target, just mark it one times and it starts.
So there is only one con point which isnt rly a point:
After you marked a target it sometimes seems that it doesn instantly start ccing it, this is a result of allready applied cc or the target is dr'ed.
all in all its a way more comfortable, you just need to know how to use it correctly