It works but expensive - FAB Defense 4 Round Magazine extension for Glock 43

Directions for installation could be better. I was worried that in trying to separate the two halves of the extension that I would break it. Once I got it together I loaded it with 10 rounds and manually worked the slide to see if I would get a malfunction, which I didn't. At the range I shot several 10 rounds loads with it and again with no malfunctions.
I doubt if I will use it as my main magazine for conceal carry purposes, because of its length. I will use it primarily as my backup mag. I gave it 4 stars because I will not be able to use it as may main mag also because of the cost. I can get 2 Vicker's 2 round extension mags for the price of this one and still have change left.