A little different perspective:
Slayerbane is better. However, the cost to acquire it is much greater--ie, a bunch of experience points.
Within a couple of levels or less, you are going to find melee weapons that are better than Slayerbane. For example -- Tagos'Axe -- Melee damage: 13 - 31; Magic damage: 2 - 6; Critical Chance: 8%
Requires Level 10; Strength 9
+5 to Magic Damage; +2 to Strength; +1 to Death Blow skill
2 empty enchantment slots
Cannot be sold, stored, or destroyed
So, when it comes to adding a crappy charm to a lower level weapon, armor or piece of jewelry, you might as well do it. Otherwise, what are you going to do with the charm? They don't sell for much. Therefore you might as well use them; you'll get better equipment and charms later on.
