I have this mirror on my full-face EUC helmet and it's fantastic. It is expensive for what it is, but I would say it's worth it.

It's large, doesn't vibrate or move at all, and it still easy to adjust when I need to. The hose part is very stiff, but where it connects to the helmet mount moves more easily. I just grab the end of the mirror and move it a bit to see more up/down/left/right when needed.

I mounted it with 3M 5952 VHB tape (https://www.amazon.com/gp/product/B07K4PQG8P/). This stuff is amazing, but it's mandatory to clean both surfaces with rubbing alcohol and don't get them oily or greasy.I also had to trim the rear two ribs off the helmet mount to make it more flexible. It didn't conform to the shape of my helmet very well otherwise. Leave the front rib intact or the mirror might vibrate.
When you stick the mount to the helmet, find some way to clamp it or set heavy things on it to apply pressure to the tape for at least a couple minutes. This is vital for a good bond.

DO NOT drill holes in your helmet to mount it.

After 2 months, the tape is peeling a bit on the edges due to the springiness of the helmet mount, but still holding strong. I might have to reapply the VHB eventually.