Have anyone tried this device from Petzl? http://www.petzl.com/en/outdoor/multi-purpose-ascenders/shunt It's not that new, It came some year ago but I havn't seen any canyoneers been using it and can't find anything about it in here. So, what do you think? Have you tried it? Would it be a good tool during rappells instead of Prusik-knots? It might be a good and safe tool for rappelling down as the "last man" on double rope?