While there are a million articles and blog posts on how to choose the right tire, chain, or jacket for the ADV market, I have found that it is more rare that you find authors recommending helmet radios. For many these have a stigma of belonging to the Goldwing crowd only. Adventure / Dual Sport riders seem to question the usefullness of this technology, and maybe rightfully so since they can get quite expensive.
Here is my take. There are two reasons to invest in a helmet radio:
1. If you group ride with a common set of people.
2. You need to sync audio with a GPS or phone into your helmet.
If you group ride then you will find the ability to talk to other people while riding a feature that heightens the experience greatly. I can warn riders of an obstacle, I can tell them I am lost, hurt, down, or just talk about the passing scenery. Its a whole new ride when you can share it all with your mates as you go. Radios are often not compatible with each other though. So that is why I say a “common” set of people. If you ride together a lot you can all decide on one brand/model to buy.
The other reason to invest in a helmet radio is to sync with your smart phone or GPS. Many GPS units have bluetooth audio now. So if you need turn by turn audio directions you can now get them right in your helmet by synching the radio with your GPS unit. The same goes for your smart phone. You can listen to tunes or take a phone call while riding as well. Now, the question of safety comes into play with this feature, so please use it responsibly. Personally, a quick call from the wife to tell me to pick up something at the grocery store isn’t distracting, its just really really handy.
Today’s bluetooth helmet radios are a far cry from the units on the market just ten years ago. Distances can get up to almost a half mile. Synching to devices takes only seconds. Noise reduction technology is so awesome that most people can’t even tell I am riding my motorcycle when they call. Speakers are getting smaller and louder. And then there is new technology like voice commands, group full duplex (many riders can all talk at the same time), and multi-hop (each unit passes the signal onto riders around them to increase coverage). They have really become a piece of technology that does not distract from the ride but enhances it.
Prices range from $50 for a chinese no-name import to $500. Below is a video review from Revzilla on a new unit from U-CLEAR that is feature packed but falls in the medium price range.
Do the research and I am sure you will find that a helmet radio should be near the top of your farkling list.
Minnesota Adventure Riders 
I bought the Sena SMH-10 system last fall for our latest Great Lake circle tour two-up. These things are indispensable for voice directions, music, and comm both intercom and phone. My lady thinks it’s too noisy via my microphone pickup inside the XD-3 at speed but I’ve linked with other folks in the BMW group and had long chats without issue. At slow speed or stopped on the other hand we love using these and talking in normal voices instead of having to flip up our face shields and yelling at each other. With ear plugs the music and voice is a little low turned up all the way but that’s fine at anything less than 80mph it’s still usable. Bonus is there’s a group buy deal via RocketMoto if your an ADV Rider inmate. Con: I got mine clipped off riding through some thick branches and stuff a few weeks ago up in Chengawatana. Pro: Sena Customer service has been a pleasure to deal with and was going to replace it at cost before I pinned down a theory of where I lost it and actually went back up to the trails the next day and found it. Since it “fell” off they have replaced it free of charge. For road riding though this thing is great and easy to use. I haven’t used the new low profile version without the easy wheel toggle but I might be interested in that that version (SMH-10H?) for GS D/S type riding considering where I lost my SMH-10b