Here is the best formula I have found for INT>Mana conversion: (for levels 50 and below)
(levelx2)+((level/5)xINT)
Using this formula you will see that at 10th level each additional point of INT gives you 2 points of mana. So, at 10th level which is more valuable? A ring that gives +15 Mana, or a ring that gives +3 INT? Longterm the INT ring, in the short run, the mana ring. Just an FYI.
He was referring to the clickable effect on the Blood Ember Arms he has. None of the flayed skin pieces have clickable effect.
For a Necro, just about any robe that gives INT would be better, once you get above 25th lvl, that is when added INT actually starts to make significant improvements on the mana pool. Until then concentrate on +MANA items and +HP items. The +HP items are very important to Necros. Their Dark Pact line of spells (which trades HP for mana) is very potent, and the more HP you have, the longer you can use the spell, and therefore the faster you will regen mana.
Man i love these sleeves. I own these and blood ember sleeves. Just like azure sleeves the AC is not quite right on what is posted on the item. When i take these off and put my blood ember sleeves on my AC actually drops by 1. So Flayed skin sleeves really have an AC value of AC22. And since My SK twink isnt close to being able to use the click effect i think ill stick with these for a very long time. :)