I bought my C3 at the NEC in November, I have used it almost daily since then, my thoughts are as follows:-
The helmet is very comfortable and has a real snug secure feel about it.
In heavy rain there is a small trickle of water down the inside of the visor, this is only when the visor is in the closed position but not clicked shut ( I guess it needs that extra mm to make the seal with the rubber strip at the top of the visor.
If the visor is clicked shut there are no problems with leakage, the front vent allows a good airflow to prevent condensation even on the coldest mornings. When the front vent is open the wind noise gets a bit louder ( this may be turbulence from my screen)
The integral sunglasses are a bit flimsy and prone to vibration above 30mph when the clear visor is open (again this may be the KTM screen height).
In general this is the best helmet I have owned, that is taking into account comfort, noise, weatherproofing and physical size (fits in topbox).
Previous helmets were N103, noisy, same water leak problem, very loose visor, better sunglasses than C3.
Arai Tour X2, Comfortable altough a bit draughty under the chin, physically very large (no topbox fit), suffers same visor leak in heavy rain, no sunglasses but the visor is a bonus.
All in all C3

