I have the medium-size Clearview with vent and I really like it.
It does NOT flex at highway speeds; I'm guessing the L and XL flex more than the smaller size.
That being said, at 5' 10" tall, I wish my Clearview was 1-inch taller; if I had to do it all over again, I would have ordered the large size. Now, I have to really "duck down" when I want full sound and wind protection. I ordered mine directly from Clearview; it did take about a month to get it, but they were a pleasure to deal with.