I went to Dalby forest as a one off last year and just used my snowboarding helmet, very similar looking to the bern one above and it did the job fine but I would have preferred more ventilation. Although I enjoyed it I wouldn't go again as I was lucky to come away with just cuts and bruises. I went over the handle bars twice, once off a drop off and the other I went flying at speed, went off a gravelly bend into a downed tree. On top of that there were numerous close encounters with trees, boulders, edges, etc. It was ace at the time but afterwards I thought about how screwed I'd have been for work, etc if I'd been unlucky as I normally am.