I installed that same GUB extender (
https://amzn.to/3A4g3D4) on my stock-handlebar MiniST2 last week and it's a very nice product. It will fit, just barely, on the straight center section of the bar on either side of the Rad's LCD display mounts, thanks to its narrow mounting clamp rings, as I expected and hoped when ordering it. Comes with shims as you may know, so it'll fit most any standard-size handlebar. I think it really is carbon-fiber and not just an imitation skin - it's extremely light and stiff. I'm not a CF bike-parts expert, but although I fastened it down firmly I didn't really crank down on it with the hex wrench to avoid cracking it. There are some review pics of people who broke the handlebar mounting-clamp rings, so don't go nuts torquing down on that end either. Those rings would be stronger if not for the cutouts, which don't save much weight.
I like it a lot, just like their terrific all-metal phone mount - well made, clamps securely and strong. It solved the problems caused by the curved and tapered stock bar that doesn't allow much room for other stuff, especially a light that has to be pointed straight ahead. Moved my GUB phone mount to it, then added a PlanetBike 800-lumen headlight and a small electronic horn that's annoyingly loud for when I need to get a rolled-up-window driver's attention. There is still plenty of room on the outboard right side of the extender to add a camera mount or other gadget if desired. At about 8" overall bar length, it's just right for me and not obnoxiously huge.
It seems to be worth the extra cost compared to other extenders and my happy experience with their phone mount gave me confidence in the brand.