Back in December of last year, I had Kurt remove the AK brake on my Shorty upper and replace it with a KKF A3 (long) brake. I had put around 800 rounds through this upper before the brake swap. He also put the A3 brake on my plain muzzle Bushmaster M4 upper. The construction of the brakes and the installation are first-rate.
The following, EXTREMELY unscientific info compares the AK brake with the KKF. I've fired both brakes at indoor (lighted and lights out) and outdoor ranges.
"Noise" is comparable between the two, and I didn't need double hearing protection at any time. Unlike another AK Shorty owner stated in another post, I did not experience any unusual discomfort (tooth rattling, headaches, nose bleeds, etc.) with either brake.
Only difference with flash that I noticed is the KKF puts it out at the 10 and 2 o'clock positions, whereas the AK was straight out the sides. I didn't notice a change in the amount of flash with either unit.
The AK brake controls the muzzle slightly better, though there's no twist to the small amount of recoil with the KKF.
Appearance is a big reason why I had the AK brake removed ....
Overall I'm very pleased with the KKF brake.
Chris