Their effectiveness sure is reduced, but when they work for you, Whip Coils will work big! Making a Bloodthirster or Keeper of Secrets strike last in combat with a unit of a minimum of S6 will make you smile and opponents cry!
Of course, if you need to cut some fat then Whip Coils should be first in line, but I mist say I've not been disappointed in my Wraiths and their Whip Coils.