I use them on the smaller pistols. They do enhance the grip and also help absorb some recoil. I have them on my LCP, Solo, and PM9... basically any 2 finger grip gun. I am considering putting them on my .44Mag revolver to help absorb some recoil and torque.
The trick to putting them on is to boil a small pot of water. Turn off the heat source and with a set of tongs, dip the grip sleeve into the water for 30 seconds to heat it up and loosen it up. Try not to touch the metal pot. Once you remove it you have about 30 seconds to get it up and over your grip or you have to do the process over again. Once it's on and it cools (about 2 minutes) it stays secure and conforms to your gun grip.