Interesting about the blowback... isn't that the point of a muzzle break? Seems to me that would be evidence to support that it works well and the absence of blowback would tell me it is not.
Or is it that you want a break... but you don't want it to work all that well, if it is at the cost of blowback?
The point of a brake is to lessen recoil and reduce muzzle rise, ie keep you on target. Some achieve that with less blowback than others. I have no experience with the Cadex but I have numerous Heathens and they do a great job of lessening recoil and muzzle rise whilst pushing less blowback (and dirt and debris) back at the shooter (and towards anybody next to him, important for 2 man teams) than other brakes I have tried. If your yardstick for how effective your brake works is determined by how much blowback you get, I'd suggest that you're using the wrong metric by which to judge it's performance...