As I've been researching mountain-bike and downhill-bike helmets I've read some interesting material, lots of it.
This article was the most interesting: http://www.pinkbike.com/news/DH-Helm...-Is-Safer.html
It concerns the typical impact sustained on a bike vs. a motorcycle, speed being the difference most of the time. I think typical trials riding fits into the mountain bike category, speed-wise.
It seems at high speeds you need a harder helmet, both outside and in, that makes sense.
However, at lower speeds, like what we usually see in observed trials, you can use a softer shell and padding which better absorbs any impacts instead of shaking our brains (what's left of them) in our skulls.
That's a layman's summary, read the article for yourself and see what you think.
I'm wondering if it's necessary for sanctioning organizations to mandate DOT or Snell approved helmets when the CE EN1078 standards have been met by the manufacturers of mountain bike helmets and when these helmets my in fact be better at preventing injuries in low speed falls.
Something to think about.