I've got a C3 , got it when they first came out (Helmetcity) as an introductory offer they were cheaper then.
Biggest problem has been fitting autocom into it...though not as difficult as into the wifes bloody C2!
Some riders report that different helmets have differing properties when on a strom (turbulence etc) and I suspect the C3 is one which doesn't go so well with the Stroms turbulence issues (I keep meaning to try out my old lid as a cmparison...) In clean air the C3 is good for a flip, however. The good points: pretty quiet, comfortable (but depends on shape of Your heed! ...see Webbike world reports) the mechanism seems solid enough, pinlock is great - a revelation! The sun visor works well, too, no distortion, but needs cleaning gently before every time you go out.
Just remembered another problem, because of the way the vents on top are routed, dead flies (and alive ones!) get dumped occasionally onto the top of your head in summer! Not nice, the worst I've had for this, ever. I fixed it by gluing a piece of cut-up plastic filter/gauze into the vent - but this shouldn't be needed on a 400 quid helmet!
Also, I haven't found a way of adjusting the clear visor so its a snug fit to the visor port seal - the C2 is better for this - and I've had some water getting in. Also, Schuberth have never once replied to my email q's (and I read other disgruntled ownes say the same!) . Just being as honest as I can be, mate!
In summary, I would say today there are other lids out there better value, and prob at least as good (and more cheaply bluetooth enabled/upgradeable, too!)