That particular magazine extension is made by Pearce Grips. I haven't shot a postal target match in many years. I always tend to fire in multiples of shots; and I don't want the pistol to move around (or, 'want' to move around) too much in my hand(s).

In recent years I've settled on Hogue, 'HandAll' rubber grip sleeves on all of my carry pistols. (I own more than one model of the same handgun.)

I've used Talon Grips in the past; but, they never lasted for as long as I wanted them to. They're also expensive. I finally gave up on them, and began cutting my own out of commercial skateboard tape that I picked up at a local bike shop.

Then I had the thumb, upper backstrap, and trigger finger areas on my G-21 nicely stippled - That modification has turned out to work very well, and given me excellent control over the gun! The following is one of my typical 20 yard rapid-fire pistol targets.