Fuck I hate these threads.....Here are some facts.
1. Every helmet sold in the USA is supposed to have at least a DOT sticker in it. Any helmet you buy directly from Europe, the UK, Australia or Asia will NOT be DOT legal and therefor not AMA legal and could present a problem at race like LL (if they check). I know in all of the ISDE's I rode they checked my helmet for our DOT certification (inside and out)
2. The guys that run the Airoh helmets here in the US can do so because professional MX and SX is also sanctioned by the FIM (a loophole I guess or they have the DOT cert).
3. There are significant differences between DOT, Snell and ECE helmets including shell matrix, thickness, EPS, chinstrap retention even eye port size. Testing methods are vastly different and I will tell you DOT and ECE are actually pretty close.
4. Any helmet purchased in Europe or Asia (especially Asia) will have a completely different shell shape and therefore fit unlike almost any other helmet you will find here in the US (be aware if you decide to buy from a Euro website).
I wont get into details but what I'll say next is only opinion however, it comes from 47 years of riding / racing and 25 years industry experience.
To me, Snell is by far the best standard we have. ECE is good and DOT is ok but for us here in the States, after seeing some test numbers, I'll take a Snell helmet every time.
I think what has been happening in the helmet world lately is amazing. 6D turned the helmet industry on its head (pun intended) and forced the rest of the industry to step up. I believe they have too. Many helmet manufacturers have upped the ante and even surpassed what 6D started. The new SE4 from TLD is amazing (I know, Ive crash tested it). Shoei is still an amazing product (also crash tested) and the new helmet with their MEDS technology looks incredible as well. I still think Arai makes a great helmet even though the tech seems old. Actually its not as it uses a multi density EPS liner that all great helmets still use! They just arent using any fancy rotational tech in their lid.
Rotational impact tech (thank you Mips) has added another level of safety we never had before and now Shoei seems to be taking that tech further. Its all great but can anyone tell me what the rotational impact standard is? We know its better but we have no base line to judge from yet. We will I'm sure, right now though we just dont know.
Anyway kids, take this info as you like and I hope it helps in some small way. I'll leave you with this. The helmet that fits you the best and I mean in every way, regardless of brand, is the best helmet on the market for YOU. Do not get sucked in by weight, what you buddy says and especially what we say on here! And never, NEVER buy a helmet just because it looks cool. Start at your dealer and go from there. Most can get you anything you want before you turn to the internet.