expandables have moving parts, and there's not one thing made by man that has moving parts that won't fail eventually. SO you need to decide if you want to risk a failure at just the wrong time, or just use something with no moving parts that can never fail.
People that use fixed blade broadheads will loose a critter they hit eventually, BUT those that fail to find an animal when using expandables will always wonder if it was the broadhead that failed, or thier shot placement sucked, or thier tracking skills suck.