fuond it to proc like 2 or 3 times in fight on EP mobs as lvl 75 mnk (capped skill, couple of merits, don't know if skill matter on proc rate). just a litle too low for what I was going to use them.
you need to hit to procc, so capped combat skill is a good thing.
Additional effect weapons procc with the same recast delay as if you had cast the spell, it can't procc earlier than that recast timer, then you need to land the hit.
