Typically, it's only a good pitch if you've got bigger hands. That's because the pitch itself should be "choked" deep in the hand. This is how splitters get their downward movement. Your index and middle fingers should be placed on the outside of the horseshoe seam. The grip is firm. When throwing this pitch, throw the palm-side wrist of the throwing-hand directly at the target while keeping your index and middle fingers extended upward. Your wrist should remain stiff.
Bruce Sutter, one of the best splitter pitchers in the history of the game, says that it is very important to put your thumb on the back seam, not the front seam. This puts the ball out front just a bit more than a fork ball. Then, he says, you just throw a fastball. A very sophisticated and misunderstood point is that the split-fingered fastball should be thrown with back spin just like a two-seam fastball. But in a Roger Kahn / Bruce Sutter interview in Kahn's book, The Head Game: Baseball Seen from the Pitcher's Mound, he points out that this is not the case.
Resource from thecompletepitcher.com/pitching_grips.htm#q3