I have two Archo's units (link)
and have been very satisfied with both (i.e. a AV-420 and a AV-500 unit).
They make a small helmet camera that fits either model. The one I've been using is very much - maybe identical - like their camera head, measures an inch in diameter and 3 inches long. Mine doesn't run off the battery in the Archos, but an external pack. Theirs works off the internal battery. On both my units the battery is a snap in affair and I carry a spare.
It helped to mount a small circular polarizer filter on the front of my camera. Without it, I often blinded the camera in the sun (it recovers quickly though). Colors look better with the filter too.
The AV-500 is a wide-screen version of the more squarish AV-420 (4:3 ratio). I carry all my tunes in the AV-420 and some movies. The AV-500 has a larger hard drive and carries more songs and movies. Personally, even though the older AV-420 is larger I tend to like it more as it has a more rugged case with rubberized corners and I can access the plugs and jacks from the end of the case; the small AV-500 case folds and covers the jacks (minor niggle I know).
I carry the unit(s) in my jacket pockets and often use a suction cup plastic sprinkler pipe contraption that sticks on the top of the helmet while shooting. The thing was made by some parachuter's helmet company (helmetcam.com ??), but I modified it enough to make it a little more adjustable.
So far the units have never skipped on me on either the GT or the RT. On the RT, I carried it in the tank bag. I don't have a tank bag for the GT (I like the looks of it without one) and just carry it in my pocket now.
I do plug it into the AutoCom and it works very well with it. Around camp time, I use it in the tent for watching a movie. Run time on a battery is maybe 2 hours video and 8-10 hours audio. I carry a spare battery almost always but think I only had one battery die since using them.
Fwiw, I must like them....since I own two!
Oh, here's a site with a lot of moto-camera stuff: Link