Sekurit makes OEM Porsche windshields and the higher prices are due to engineering, quality, import duties, etc. Sekurit has won a few patent infringement cases against other glass manufacturers for copying and stealing some of their proprietary designs and tech.
I joked with a fiend that Pilkington glass is called Pilkington because that is the sound you hear as it breaks the first time even the smallest pebble is thrown up from another vehicle and makes contact. I'm sure they make some quality products but when my insurance co replaced the glass in the Boxster they demanded the lower cost Pilkington glass and it lasted less than 30 days. The second time around I had a pretty good case to demand OEM and never had another issue. Coincidence? Perhaps.
My wife's Honda had 3 Pilkington windshields before we convinced the insurance company they were losing more money than they were saving with cheap replacements. Replacement OEM Honda windshield was still on the car when we traded it in. Draw your won conclusions.