3.4% increase in damage over averages, 3.4% increase in damage over max critials. Right in line with the 3-4% increase he proposed with his tests. This basically means that Pole Grip remains the top grip to use for almost any situation, and leaves Brave Grip as worthless (unless you count NPCing it for 1,100 gil).
Please, if you're testing, post the exact mobs you're testing on.
Because of how critical hits work, if this is an increase to the attack/defense value you will see no difference on monsters with much lower defense than your attack. Not a single comment here even mentions it, and from the numbers you're getting you're most likely testing on much too weak opponents. Easy Prey at the very least if you're testing please.
It's pretty much X's knife effect. Amazing for raging rush and drakesbane, and I guess tredecim scythe users. Also awesome for mighty strike zergs (when you don't have an alliance of kraken DRKs!).