I usually forget i have them to be honest but when I remember I usually get drops...first week of CoE I tried one for each boss one just at the first and one just at the last and one time I only tried it on SYLOK THE DEFILED!!! Once right before he died and got a drop same with the servitor [spoiler]I stopped popping them like molly's and noticed more drops[/spoiler] I didn't notice an increased chance at all with the different uses but I did use one just before they died and usually get one