"I've seen enough issues with enough brands that my default response to the question of "what mag extension for a G43" is "a different gun"....
The above is QFT!
The vast majority of glock aftermarket stuff is not reliable or is reliable..until it is not. FWIW, I would not bet my life or the life of somebody I cared about on the reliability of an aftermarket mag extension. I would choose to go with a factory mag or pivot to another gun if capacity/grip size was driving the train. YMMV greatly.