I have never had one of these mounts fall off even if they do not have 100% contact to something. I have bought knock off brand ones before and they are awful. Just get these and save yourself the hassle.
These things really do stick to just about anything. Just make sure you clean the mounting surface before application. Also if you plan to mount directly to your machine make sure you put in an area that won't pick up vibrations. Mounted a gopro to the radiator cover of a banshee and ALL footage picked up vibration from both the engine vibrations as well as the paddle tire vibrations.