I recently got two TW leather grips (the thinner one and the thicker one), and a Wilson leather grip. I put them all on (I have four of the same racquet), and within a half-hour I started getting three blisters on my racquet hand: one on the bottom digit of my ring finger, one on my base of my thumb, and one on the heel of my hand.
I find this amazing considering that this season I have been playing using the stock grips (Wilson Micro-Dry Touch) for months, hours at a time with no blisters.
Also, three fingers of my racquet hand felt a little numb, though this went away after several more more days of playing. I think I am going to go back to the Wilson Micro-Dry Touch grips. They provide nice cusioning, very good tackiness, fairly good feel for the bevels, good ridges and valleys, and no blisters.
Is leather worth it?
In the end, the aggressive all-court player always has the advantage against a power-bashing baseliner.