Swebb, the C2 is the replacement for the Concept which has been out for quite a few years now, hence quite a few bargains to be had on the Concept. The C2 has improved aerodynamics and ventilation as well as a better locking mechanism - whatever you choose, both helmets fab. I personally went for the C2 as it was more 'up-to-date'. Have just got back from 150 mile jaunt down to south coast and am chuffed to bits with the lid. Although very quiet, I dont think you will get quite as hush hush as a full face, but then again in the summer you cant open a full face and you can with the C2/Concept (although you shouldnt ride with it open it says in the manual).
Happy decision making !
Martin
54 GS and lovin' it !