Heya,
Tested this thing out to answer some questions I had concerning proc and such. Fought over 100 EP mobs in SSG as THF/NIN, and here's what I came up with. If the data seems obvious to you, I apologize.
Proc rate stacks on top of Triple Attack rate, i.e. you get the 5% from the earring DA, plus your additional TA rate (in my case 5/5 merits+base 5% =
10%; 15% cahnce of a multiple attack).
Triple Attack and Double Attack do not compound, i.e. no 5x attack. An un-protected Sahaigin face-to-face using Assassin's Charge and Dancing Edge would take 1250-1450 damage (identical to what it did before I had the earring). This gathered from over 100 ws's, not like the bulk of these yo-yo's posts who poll from 10 or so trys and make a bogusly definitive result (e.g. "I fought 6 mobs, got the drop 3x, so it's a 50% droprate" ><).
All that being said, this earring well worth the cost (I spent 587,500g on coins on Sylph), and greatly improves your damage/sec over the course of a few mobs. I can't see how any DD would choose a different earring considering your 2 optional slots (would be tough to give up a suppo or my bushinomimi if there was only one), but that's my two cents. Hope you found this insightful.
Edited, Nov 24th 2008 4:53pm by Lucretius