The short version: Don't buy one.
The long version: Really, don't buy one. I have a C3 Pro I've been using for the last 6 years and finally decided to replace it......mainly due to the in built speakers losing the right side when the flip top is open. No other reason.
Bought myself a brand spanking C4 Pro from a well known supplier and it first seemed lovely. Really plush interior, well fitting, great stereo speakers, MUCH better positioning of the microphone. All looking good. However, it was a hot day with heavy traffic and I, stupidly, decided to go home on the A30 rather than the M3 and didn't get over 40mph and had the front flipped open the whole way.
Then, a couple of weeks later I took a trip cross country and oh my frickin christ.....
Firstly, the wind noise compared to the C3 is deafening. At 100mph you can't hear the music anymore. Maybe I was spoiled with the C3 but holy crap the C4 is loud. Schuberths own website states the C3 Pro is good for 85db while the C4 Pro came in at 89db in testing at....whatever speed their wind tunnel was set at. Who knew 4 decibels was so loud.
But there is something that's even louder......on the way back it had gotten a bit chilly so I closed all the vents to discover that the top vent makes a loud buzzing sound when closed. So loud, in fact, that it was drowning out the wind noise. And what's more......the visor won't crack open a little bit, it's either closed or open 2 inches. The buttons for the in built electronics are in stupid positions and the daft velcro tab thingies that are supposed to go under the chin strap just keep catching on my jacket and are going to get cut off with scissors very bloody soon.
A snotty email to Schuberth exclaiming my disappointment resulted in a very long email back which basically said "It's not our helmet, it's your bike". I'd return the damn thing but the 'policy' is that a helmet that has been worn on the road is now used and cannot be returned and 'we recommend trying your helmet on indoors before heading out on the road'. Helpful that.
So instead I'm going to take some retribution out by recommending to anyone that'll listen not to buy a Schuberth C4 Pro. I just wish I could not recommend a C3 Pro either but I'd be lying, they're great.