Shock loading is bad and should be avoided at all costs. An anchor moving an readjusting an extending is bad and introduce problems such as loss of control of belay.
Having the force of a second fall on only one piece is no issue at all. Pieces generally don't fail because of excess load they fail from poor placements.
So stay away from the sliding-x unless you need to equalise two pieces of marginal pro. (ie RPs and other <5kN pieces)
(This post was edited by patto on May 6, 2014, 5:45 AM)
