I have them all in the Glock 22, 40 SW. They start with 3rd having the groove slide on rail at the bottom of the receiver. The RTF 2 improved grip, with a little smaller grip and kind of raised dimples for a more secure hold. Gen. 4 comes with a smaller grip and two optional larger back straps, A larger aberdexerious magazine release, and a double recoil spring like the sub compact Model 27 I have. A much better fit for my short stocky fingers, larger mag release, you can drop the mags without shifting your hand, and the double spring seems to soften recoil. The Generation has much improved at the same price!