I have not read anything about how "realistic" their testing proceedures are, but so far they look pretty good.
The real cool thing is being able to pick a helmet, or for that matter a helmet maker, and not only get a rating on a particular model, but a graphic of the helmets strong and week points.
My helmet, a Shoei RF 1000 , (has a different name in the UK) got three stars, they cited a somewhat poorer rating in side impacts, while front and rear were rated good.
This was in fact better than a 250 dollar more ARAI helmet I almost got....but I should point out they both got 3 stars. So do compare impact test particulars, as there can be two helmets rated the same, but still have one that did better. ( Just the problem you run into when using only a 5 point system, you have to bracket the results somewhere. I would preffer a "total point" rating, but that's me)
Again I shoud point out that how well your helmet fits is vastly important, that 500 buck Arai is not going to live up to it's potential if it does not fit your head right. So seek help from a someone trained if you are not sure how the helmet should fit.