I have the Miculek comp on .223 AR.
It is not so bad shooting it, behind the trigger, but stand off to the sides and it really rattles your dental fillings.
The USPSA has it's own publication called the Front Sight. Somebody had done an experiment with different comps, a laser designator/pointer, and a camera with a very slow shutter speed. The laser made more or less of a squiggly up and down line on the target depending on which compensator/muzzle brake was screwed on. A Caldwell Lead Sled was used to eliminate any undue influence of a human shoulder behind the rifle.
I would also like to get an AR in .308, so your review was right up my alley. Thanks!