I figure it this way.
https://m.youtube.com/watch?v=lR-CYmPPGwA
While the surplus mags are great mags - they WILL break in certain situations. They aren't steel. Are they still good value at $30 and unissued? - yes.
The polymer CSA mags are super and outdo the Bulgy AK mags which are considered by many (not me) to be the gold standard. The CSA polymer mags MAY be the best x39 mags in the world.
The only thing in that video is a the feedlip drop test. You can engineer any mag to exceed in one dimension vs. peers...
The fact of the matter is that mag inserted into the gun and dropped will sheer the CSA mag's poly mag catch and render it entirely nonfuctional. That poly mag is also much more likely to be destroyed in that scenario than the aluminum mag -- why nearly all serious use AK mags, including Magpul's premium, have steel reinforcement of the mag catch area.
The Vz58 aluminum mag may dent and bind the follower when dropped while in gun if impacting side, but it can nevertheless be disassembled and refurbished, and its mag latch is substantially less likely to sheer vs. poly that may also scrape sufficient material off to become nonfunctional even if not completely breaking.
*I'd also argue that since less surface area interface (Vz58= roughly 1/2 of mag width vs. AK effectively full mag width), the Vz58 poly mags are even more likely to sheer if dropped than equivalent AK mags, where such an issue is a known and indisputable problem.
The OEM alloy mags are also lighter than CSA poly IIRC, and unlike AR15 milspec aluminum mags that remain military standard issue to this day, the OEM alloy Vz58 are roughly 3x as durable due to thicker material (and I'd argue superior shape/stamping with respect to ridges, insets, etc. that all increase stability/durability over just a flat stamp) and required none of the lifecycle improvements that the AR15 mags did during the GWOT for the AR mags to become truly combat-reliable.
In sum, one test by the vendor of a competing product does not prove that that product is superior -- Magpul's done rebuttals of Lancer/ETS/Hexmags (and perhaps others) on the AR forums, with their attempting to game cracks/splits/etc. when dropped, and Magpuls still functioned in magwells even when broken... And their reduced flexibility was designed for certain things including (IIRC) less degradation from DEET/insect repellant, greater operating temp range, and other specs that affect overall reliability in normal use, instead of prioritizing torture test performance by opting for a softer/more flexible polymer like their competitors...
To be clear -- I don't fully subscribe to Magpul's assertions, and most my poly AR mags are Lancers, but I will grant that I do believe Magpul's philosophy of design is coherent and their claims more right/accurate than wrong/misleading...
**Lastly, do want to note the CSA Vz58 mags appear to be made from the same or similar polymer as the early CZ Skorpion EVO mags that were notorious for cracking and other long-term reliability issues. Transparency in poly mags always comes at a substantial cost, as it limits fiber reinforcement/the skeleton of the surrounding polymer body itself.
YMMV.
