if you read the "open hand - crimping" thread here on this section, you'll get plenty of info.
in my opinion both prehensions are dangerous, if you pull really hard. crimping is mostly dangerous for pulleys and joints, openhanding for wrist and forearm tendons, in my experience.
practice both, remembering that each climber has a preferred/stronger prehension. you can't perform at your best on everything. there's Ondra already for that.