Arrendondo mag extensions are the only ones that I would use if I were going to install any extension that adds over 2 rounds to Glock factory mags because of the spring situation mentioned above. Yes they aren't cheap, but if you want the mags to actually work and last, then it is worth it. Personally I have factory mags with +2 extensions or the factory 22 round (40s&w) or 33 round (33 round) mags.
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