A product barely relevant to adventure travel, but I would like to share my experience.

Schuberth C3 - Expensive, rain leaks down the back of the visor, visor scratches very easily, internal sun-visor mounting points are flimsy, break, and are not user-serviceable. Generally very disappointing.

Schuberth SRCS bluetooth headset/intercom/FM radio for the C3 helmet - Great sound when it works, which is hardly ever. First one wouldn't even turn on. Straight back to the shop for an exchange. Second one burned out a speaker after 2 days. Return, exchange. Third one burned out a speaker after 3 weeks. Retailer out of business. Contact Schuberth. Told to contact distributor. Contact distributor by phone, email and letter without reply. Months later, retailer re-surfaces under new ownership. Return, this time for a warranty repair. Wait 6 weeks. Get the repaired unit. Speaker burns out after 2 days....

Even when it does work, the radio reception is utterly useless. Spend hours trying to get a signal. The RDS function is utterly useless; Unless you manually store a frequency it will never manage to re-tune. Note that they've now brought out the C3-Pro helmet with built-in antenna, so they must know the reception is rubbish.

Even when it does work, the bluetooth connection drops out all the time, requiring an endless cycle of switching it off and on again, then switching the GPS off and on again.

Even when it does work, the stereo bluetooth profile craps out and reverts to a crackling, faint mono.

Even when it does work, the microphone makes it very hard to close the helmet properly.

I would strongly advise against buying it.

I would love to hear recommendations for a good bluetooth headset, ideally with built-in radio.

In using the Sena SMH-5 but haven't had a lot of time to use it before winter spoiled all the riding opportunities with my wife. I can say that I found the (small) speakers that it comes with are too quiet to hear clearly over wind noise at highway speeds but there are larger ones available. The kit I bought came with boom mikes and one of them made horrible crackling noises caused by damage I caused installing the mike under the helmet liner. I bought the wired mikes designed for full face helmets and they work perfectly now. I didn't pay an awful price for them so I pretty satisfied with the purchase. If they fail this year though, I will be pretty disappointed. I don't expect them to last forever but it would be nice to get 2-3 years of occasional use from something you pay a not insignificant price for.

Scala ones last well enough but the sound quality and volume is garbage. Intercom function is limited to under 40 mph.*

Personally, I'll wear earbud type phones for the radio/noise cancelling, watch rather than listen to the GPS and stop to call back anyone that phones me.

* I am working on a bit of bodgery. I'm going to strip the speakers and sew them into a balaclava with quilted bits over the top. (The old home economics class didn't only helped me meet girls when I was 14!). If the thing is wearable the speakers will be right over my ears, inside the soundproofing and the BT unit will hang down the back in a pocket under the edge of my lid, maybe in a plastic cover. Report back in a week or three.

Andy

Bought 2 C3 Pro helmets and 2 SRC comms systems for the wife and I.
Overall impressions: mixed.
My helmet finish was not good. There was a section of plastic moulding behind the visor (upper side) that was not seated sufficiently. When you observed it looking into the visor it had dropped by about 6mm compared to the right side. I was not in a position to send it back as I brought the helmet with me to NZ from the US.
The second issue was one of the SRC comms units. It would not work on the VOX setting (i.e. would not voice activate). The second unit worked perfectly. I sent the unit back to the US for repair and have since received it back. The problem still exists. I have my doubts whether the unit ever made it from the retailer to Schuberth.
Other impressions:
Comms system works very well (except for VOX). Bluetooth no problems.
Helmets dont leak. Slightly more quiet that my Shoei XR1100 (I still wear ear plugs and can hear the speakers fine). Good fit however leaves slight dent in forehead but find it more comfortable than the XR1100. I like the way the SRC fits into the helmet with no exposed wires etc. Charge up is simple and battery life pretty good. Cell phone works well on blue tooth with no issues. The retractable sun visor is excellent. fog free system works very well. Helmet is not light but I knew that before purchasing. The flip up system works very well. Don't think the strap system is great (prefer the D rings).
Would I buy another one. Yes.

Got caught up in the C3 hype two winters ago, can't seem to get through the off season without buying something.
I like the fit and feel of the helmet, it's hard to tell how quiet it is relative to others, I think they all fall into a small range of decibels. The paint is thin, I can say this because of a long scratch of unknown origin, the visor has scratched but I had to fall off into rocks for this one. Had trouble with the sun visor almost right away, it's quite a flimsy affair, having just shelled out $800 I got pouty over this and after dealing with Schuberth got a new helmet and it is starting to give the same grief again, find I don't like the sun visor when it is down anyway, it shakes at even moderate speed so you are looking through vibrating bug dooy to far away from your eyes to focus through.
Saved the worst for the last of this little rant. The visor will not stay up. I found out to late that it is designed to close at 30 kph, I like the visor up at all speeds outside of rain/dust and can't live with this. I have tried O-rings, stuffing it with gummy bears and sand paper but can't get it to work well enough. This being said I am having trouble finding a modular helmet with a stiff visor.
Al