I've used Go Pros for a couple of years to film in car shots during rallies and to film car reviews, filming both behind the wheel and with cameras attached externally on suction mounts. But I'd always borrowed them and when looking to buy my own POV, the features of the Drift HD made it far more attractive.
The remote control is a must in a race car when you are strapped in and the position of the camera makes it impossible to switch on a Go Pro. Remotes can also be used to trigger multiple cameras if needed. I guess the same applies on a bike. It's easier to press a big button on a remote than a small one on the camera. The remote buttons are big enough to hit accurately with a gloved hand.
You can simply plug in an external mic on a Drift. Great for use on a bike with a $25 lavalier mic under the foam, or can be attached to a race car comms system in seconds with a Drift supplied adaptor. Can't do that with a Go Pro and good sound makes a HUGE difference to a video image.
The built in viewfinder may be small but it's there! It allows you to line up a shot, not guess at what's in the picture and only find you were wrong after 30 minutes of filming.
Being able to mount the camera body in any orientation and then swivel the whole assembly internally until your horizons are level is a great feature
The Drift HD uses a standard 1/4 inch thread mount, not a custom mount like the Go Pro. So it fits any tripod, ball head, monopod, Gorillapod etc.
The control menus are in English (or half a dozen other languages) so you don't have to memorise some random code and remember that it means you've dropped the frame rate or switched to stills mode.
I've not used either as a helmet cam but it strikes me that the shape of the Drift, which is more 'streamlined' tha the Go-Pro, would tend to minimise vibration a little. The Go-Pro sticks out 'flat' into the wind, and whilst the Drift is hardly the perfect teardrop streamline shape, it's a lot closer to it than the Go-Pro. This is just an observation - I can't verify it personally, but I've had the Drift working well when mounted on the boot of a car at around 140mph and the images have less vibration than I'd have expected. I'm told the suction mounts are "good to about 150mph" and I've never been tempted to find out! Well, maybe a little.....but I've not done so yet.
In every respect I personally find the Drift HD more conducive to actually making a decent video, and I've used the Go Pro a lot more in the past than I have my new Drift. Go-Pros may have the name but I reckon Drift have thought long and hard about making a better product.
NB I have no connection with Drift, I'm just a big fan!