Engineer Flamethrower Bugged to Death
I tested the Engie flamer today.
Deadly Mixture sure does work. I tested on Corrupt Ice Formations as they cannot be critically hit and do not accumulate Bloodlust (which I have equipped on my weapons).
Without Deadly Mixture, I was hitting for 2490, with it I was hitting for 2910 with a single burst.
Juggernaut however is indeed bugged and does not grant toughness in the stats table.