So a stone caught the corner of my acrylic lip extension the other day and I'd been looking for a reason to buy a taller screen anyway. Years ago had a tall Parabellum on a R100RS and thought I'd give it a try on the GT.
My impression was the same as just about everyone else. Nice enough screen, but the mounting hardware is pitiful (that's being generous). The real issue is the metal through nut and the worthless rubber washers that are supposed to go inside the factory mounting arms and on each side of the parabellum angle bracket. The whole arrangement requires over tightening the screen bolts to keep it "sort of" aligned. Even then it doesn't work very well and the angle brackets want to squirm around.
There's a easy fix. Quick trip to the hardware store and you can make a huge difference.
For each mounting bracket you need a plastic panel joining screw (you're just going to use the "nut" side (trimmed to length), 4 nylon washers (used 2 different sizes to get the thickness I wanted), and a stainless button head screw.
Goes together as shown in pictures. Makes a huge difference.