if your INT/MND is higher than the monster's INT/MND+10, then +1 INT/MND = +0.5 macc. If it's less than, +1 INT/MND = +1 macc. +1 enfeebling skill = +1 macc.
Therefore, at worst, this is 1.5x better than a +2 INT/MND earring, and at best, 3 times better. However, it doesn't affect potency like MND does for slow/paralyze.
A good balance between potency and skill is key, but consider the fact that +3 skill in an earring slot frees up +3 skill elsewhere to add potency. For example, a communion earring and avocat pigaches gives you +2 MND and +3 skill, while an enfeebling earring and mahatma pigaches give you +6 MND and +3 skill.
In terms of enfeebling magic, theres a fine line between sticking, and resisting, theres that line between 100% resistant to sleep imps, to sleepable ims, an Omega that can be enfeebled without ES, and an Omega that can be enfeebled without ES... While 3 enfeebling magic may be not worthwhile to some, and for many people its true, it can also be your make or break piece.
So for the casual RDM, not really worth the price tag, if you find you have no problem sticking possible buffs on whatever it is you fight than not necessary. But if your having trouble, this is the piece for you.
Try to go for ra/ex pieces like pigaches first, if they dont solve your problem here is your answer hopefully.
Amazing piece of equipment in the level cap fights and while leveling. outside of level caps and 75 merits, some rare/ex equips, and the enfeebling torque should make enfeebles stick almost always.