Richard, I can't hear it at high speed. I wired a helmet with a tiny speaker, and got the module to plug into. Still couldn't hear it reliably at more than 100mph. Some guys apparently can. My ears have been abused by a lot of loud noises, so maybe I'm not the ideal judge. At lower speeds, like around town, I hear it fine, even without the earplug. I gave up on the earplug, but it might work for you.
Regardless, when the unit is mounted as I described, it's highly visible, and I can usually spot the light instantly. When I'm at really high speed, I'm crouched even more, so the unit is hard to ignore.