Great news!
I've tried it out, and everything seems to be working okay, but with one small problem
When testing with a rogue with both the savage attacker and piercer feats, it seems to deal damage when you roll damage against a target, instead of waiting to check if you want to reroll - but it then also asks if you want to reroll with piercer and deals damage *again*. Essentially rather than rerolling the damage using piercer, it rolls the dice again and simply adds that as additional damage on top of the savage attacker damage roll. Screenshot included to show you what I mean.
Attachment 61386
In the attached image, the yeti *should* have taken only 10 damage, but instead, it took 21.
I've confirmed the behaviour isn't due to other extensions, by running an instance with just Theogeeks Improved Criticals and this extension loaded.