I don't own one (yet)  and dont' really wear one going for a chilled ride by my self.  as soon as I get with other riders and the bar is raised, I'm trying new things then i'll borrow my mates.  I still feel like a tw*t wearing the typical MTB lids.  need to get me a piss pot.  the only time i needed a helmet (and was wearing one), i flipped my bike and landed on my sholder/head on the edge of a curb, the helmet i was wearing,   cracked, split and impailed the back of  my neck. it was a Met.........something from Halfords.  if any trials rider should wear one, it should protect the bk of you head/neck.  but then again if you doing low risk manuvers your more likely to shin-dig.  I (almost) never ride with out my 661 shinnies.