We took an AR-15 rifle with a standard "birdcage" brake and shot several groups, then switched to the Dragon SpitZlead brake and shot again. 
Same rifle, same day, same conditions, several types of ammo, etc. and ranges were from 25yd to 100yd.
The groups were close, with no statistically significant difference between the groups.
Overall group averages were 0.59" for the birdcage, and 0.54" for the Dragon SpitZlead. More due to human error than mechanical.
This may not be true for every rifle, ammo, etc. but it should be correctible (sight adjustment) if there is an initial difference.
Below are a couple 5 shot, 100yd groups, and the rifle used in this experiment.
Standard "Birdcage" Brake at 100yd Dragon SpitZlead Brake at 100yd