Triple Threat relies on your main hand weapon being thrown and light (Dagger, Francisca, etc) if you intend to dual wield for more damage, but fhe off hand notably can be any light weapon, even if its melee only (i.e. Dawnsword).
Thus if you're mainhand weapon is throwable, I consider it better than Evicerate since both will do 6 attacks, but Tripple Threat only has an accuracy drop not a damage drop. plus you can staggar enemies. Evicerate's +50 evasion afterwards is nice, but only lasts a turn so you will need to do some considerable buffing to make the damage worth it.
However if your mainhand is not a throwable weapon, Evicerate is really your only option.