For three mana, that's not the greatest rate in the world, but there are plenty of targets in multiple formats, and finding ways to get more interaction into your decks is always good
Maybe its time to play Errant and Giada flash again
I forget why I asked it to suggest a similar card, but it seems to improve results, I speculate that it helps anchor the model
Take Ugin, the Ineffable as an example: Colorless spells you cast cost less to cast. As long as Ugin is on the battlefield, your colorless spells will be two mana cheaper
Sadly, this card works with Flash but not instants
And An Offer You Can't Refuse trades a dangerous spell for two Treasures, an often acceptable downside when you deny a key spell like Ad Nauseam or Final Fortune