I would never use a shackle at the clew for sheets. But for a halyard at the head? How's that going to be swinging at your head? My mainsail halyard has a shackle that I can't imagine attacking me. My headsails are roller furling and stay hoisted - shackles there are no threat. The spinnaker halyard has a shackle and could possibly be a threat but it has never happened, not even close.