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In general, the more clear the plastic is the more brittle it is.
In practical use, I have never heard of PMag failure do to the plastic in the window, and unless you plan on starting a land war in Asia, I wouldn't worry about the Lancer mag either.
Take a look at the ETS mags as well.
I have found them to be quite good, and use the for .300 BO just so I can see what is in the mag at all times.
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The ETS mags are tough SOBs, but there's a caveat. They have a version with a mag coupler molded into the sides of the mags, allowing you to twist and lock 2 of them together without needing a coupler, but the molded coupler makes the mags wider, so they're difficult to insert and extract from doublestack pouches.
Even the non-coupled ETS mags have ribs that stick out quite a bit, making them a tighter fit than any other mags I've used (PMags gen 2 & 3, Lancers and GI), and yanking one out of a doublestack pouch is difficult, and will usually yank the other mag out too, when the ribs catch on each other.
Lancers are my favorite 5.56 mags. Gen3 PMags are GTG too, windowed or not, but the Lancers steel wraparound make the lips more spread resistant, and more resistant to splitting the rear when a full mag is dropped.
I haven't tested the smoke vs opaque Lancers to compare toughness though.