What is different between the two?

G21 Gen4 and G21 SF? On the Glock webpage the dimensions look simular

 

The SF grip is slightly narrower up where the frame meets the back of the slide. It might be a little thinner all the way around - you really have to hold the two to feel the difference, but there is a difference. Meant for smaller hands to to get a higher grip on the gun a little more comfortably. That's where I notice the difference at least.

 

Thanks, so basically the SF will be better for me, I don't have large hands.

 

It might...if you're able to hold each version you'll know which one is better for you.

Here's a better picture of the difference between the two.. scroll down a little way to the picture of the two side by side looking at the mag well.

https://www.ar15.com/archive/topic.html?b=5&f=13&t=138955

 

You helped a lot, thanks man.

 

The Gen4 is the evolved form of the SF Glocks. The benefit of adjustable backstraps is to find what size works best for comfort without having to specifically look for standard or SF Glocks.

 

IMHO the 21 is the best of the Gen4 Glocks. I had an early Gen4 22 that I never cared for much after I got the Gen4 21. This 21 compares very well to my HK45 and my 1911's, including my Dan Wesson Valor. I don't see the need to give up my Gen3 17, since I prefer to keep this 9mm rather than trade it for a Gen4.