As of patch 3.1.0, you have to be level 50 or higher for the enchant to become active. If you had Clefthide Leg Armor applied on an item before the patch and are below level 50, the following message will appear in red: "Enchantment Requires Level 50" and the enchantment will not become active until you reach the required level.
Note also that applying this kit to an item now causes the item to become Soulbound. The old practice of having a level 60+ apply Clefthide Leg Armor to a Bind on Equip item and then return them to another character no longer works. Instead, the kit must be applied by the character that intends to equip the enchanted leggings. You must be at least level 50 to apply Clefthide Leg Armor.