it should just turn the next non crit auto you deal into a crit. so as to not interfere with crit chance.
a duelist melee shouldn't be deincentivized to get some crit chance if she should wish. since what if that one auto were to have been a crit anyways. there's overlapping taking place.
with the attack speed boost she gets this shouldnt be a problem to do.
NemeBro2 votesFiora should definitely get an infinity edge, since the 250% damage crit applies to the second hit on her E. This is a guaranteed crit on a 4.2 second cooldown if you have 40% CDR.
LilxPaprika1 votesNot necessarily.sure +50% is nice but your not getting most out of 1200 crit chance investment.
Come to think of it 
should also get changed to reflect this. On his q should also be his next non crit basic attack is converted into a crit.
Tbh get IE and another crit item. With the auto reset and 50% as boost on two next auto and as from items. You crit at least once ever 3 autos or less. Guaranted crit every 1.5 sec ish... You don't need CDR for crit. Just as+ auto reset. Sure the CDR helps but shouldn't overlap.
There's still overlap. Say all you get is 20% crit chance. You have one in 5 chance to crit if that chance happens to be same time this spell works its as if you doing have crit chance. Its as if your 1200 gold investment in crit chance was non existent in this instance. Its not that likely to overlap but can still happen.
Or is RNG factoring her e into the equation.