[updated]I decided to stick with the Corsair's Knife after about an hour of using the Kidney Knife. The critical hits didn't kick in that often and the damage it did was significantly lower.
I'm currently using 2 Corsair's knife on THF but I'm debating on switching over to Kidney Knife. Does anyone have any recommendations or experience with the Kidney knife? Does the critical hits make up for the loss of attack?