Turn 1: True Strike (action). Off-hand attack (bonus action).
Turn 2: Main hand attack (action). Off-hand attack (bonus action). True Strike wears off.
So there you trade off one attack for Advantage on three attacks.
So your 3 attacks with advantage on the hit are better than 4 attacks? No saving through or wisdom roll required on the True Strike cantrip from Elf racial or Mage Breaker?
Does true strike add to crit chance? That would be a bonus...
But...if your first strike after casting kills the target, you're back to using/wasting a main hand attack or bow shot to re-apply to another target. So if you're ranged primary or 2-handed or shield + weapon, there's basically a whole turn wasted before you can do damage. Or again, if someone else in the party kills what you've cast on...it's wasted.
~War~