Okay, let's say you need to roll an 11 or better to hit.
Without this, the Avenger has a 39/400 chance of rolling a critical, and a 261/400 chance of rolling a hit.
With the ability to crit (or even auto hit) with this, this changes the math (GAH)
Dear gawd.
Seriously.
I just woke up.
Look, it gives Avengers who have a retarded amount of accuracy as it is even more accuracy and makes their critical hit ability as good as the daggermaster's.
Except, of course, the daggermaster misses if he can't hit with his crit. (This isn't really a good argument tho, as if you can't roll 18 naturally and hit something your DM is a dick or you got debuffed to hell. Or you need to run away. RUN AWAY DAGGERMASTER RUN THIS IS NOT YOUR FIGHT OH NOES THE PALADIN GOT EATED BY VECNA NOOOOOOooooOOOooo!)
But seriously. The Avenger doesn't need more autohit. I dunno if it's broken, but damn if it isn't completely off the hook.
But regardless, if you give this the autohit ability, you're staring down a daggermaster with an execution axe. Those crits ain't with a 1d4 weapon. High Crit comes into play here. Massive damage.
It won't be pretty.