when seeing online comparisons it's always hard to judge not knowing what the settings, conditions and how much post processing was done. It would be easy for a pro to make one camera look or sound better compared to another if they wanted.
The audio is definitely better with the external mic being used, with the mic taped to the back of the helmet. I have mine set at the low "one bar" input level setting on the camera and rarely use the external mic out of laziness.
You can tape some foam over the onboard mic to help with wind noise, but in the end it's a little crappy mic on most of these cameras and going down the road at speeds there will be wind noise, at least from my experience.
I've had a few various helmet cams over the years, none of them have a large enough sensor to really have great low light shooting, all of them seems quite noisy when the sensitivity gets bumped up. For the most part most look great in good lighting conditions, and look not so good in low light. There's post processing that can be done to help with the noise, but you can only polish a turd so much... for me making MC videos is something I really don't want to spend much effort doing, I do that enough while doing video work on shows. I spend far more efforts in my photography usually when riding, but it's fun to have some short videos to look back on after a trip or share online. Easy to make in iMovie with little efforts and time once you get the hang of it. I use it more than Final Cut Pro just for simplicities sake for bike vids.
Here's a somewhat boring clip shot with a HD 170 in challenging lighting conditions and some night riding, no post processing, no external mic, just crappy edits. For my purposes the image/sound quality is good enough to share online. I find the mic on the ghost to be just about the same, I keep it on low input setting for shooting while riding.
In the end the content of what you're shooting and the editing will make a video "better" to document and share your ADVentures than having perfect image or sound quality IMHO.
Death Valley 12/12
from Lost Rider
This video also a HD 170 I was using an external mic.
BMW F800 R in the Malibu Canyons
from Lost Rider