I've used HARD for years. In my Arai I was able to mount the receiver to the chin bar inside. There was plenty of distance between it and my chin. Did a 90 mph get off with it and no injuries above the neck. On My Shoei, it's too close for comfort so I placed it on top of the cheek pad. I have velcrow on the receiver and it sticks to the material the cheek pad is made of.
As far as batteries go, if you're careful to turn the receiver off EVERYTIME you stop riding, the batteries will last for months riding every weekend for hours on end. Same with a distance trip. You can easily travel from CA to NY on one set. I carry a spare set of batteries with me in case I forget to turn it off.
The light should not be in your field of vision. I position it in my peripherie. At night though, it is bright.
Hope this helps.