afaik,
all Arai shells are the same.
the construct inside varies e.g;
caucasian / asian.
Snell is the highest recognised standard.
technically - yes you need the "EU 2205" sticker to be legal here in the EU.
i would argue if "nicked" for ir - but it's never been checked - though asked about it maybe, 2 or 3 times in over 30 years. - in U.K. not Ireland.
note though that the "science" of helmets is far from perfect - labels and brands names
might mislead you - i.e; pay lots for a top shelf lid = safer than less bucks and lesser known brand.
the best way to test a lid is on a cadaver and replicate the circumstance that made the head hit the deck.
then examine contents to see what happened at impact.
then design to lessen THAT.
but that isn't socially aceptable apparently, so that kind of research is limited.
good fit, obvious shock asbsorbtion quality as opposed to "comfort padding" and "faceted" shape to lessen chance of head rotation and neck twist upon impact is about all we can hope for and look for in a lid.
so, thats impact and "twist" looked at.
another aspect is the damage caused by the brain rotating within the skull - like a boxer getting a right hook -the head moves so fast the brain doesn't keep up as the the head turns rapidly.
a relatively common brain injury.
how can
any lid cope with that
sorry - off topic and a bit dark maybe, but it's a pet peeve of mine

.