I have carried Glocks for years now, pretty much 24/7. These include the 21, 30 and 19. I to help with the slick nature of the grip on my first Glock (Gen 1,model 19) I used a piece of 2" bicycle inter tube. I would cut a piece of tube to be a hair longer than my grip, and pulled it up and over the grip. I then used small scissors to trim it in. One piece would easily last me six months on the street/everyday carry. One tube lasted me several years. The same size also works on my model 21's and 30. Besides being inexpensive, the rubber is tacky to the feel (even when wet), very thin so it doesn't make the grip any bigger and since it is black it blends in well on the gun.