Fox quality is generally good, never perfect, in my experience and opinion. A majority of their designs simply don't appeal to me, but of the models I do have, there is always some little something that rubs me the wrong way..
Terzuola Original Gangster Ti - blade rubbing ever so slightly against show side scale despite being evenly centered, section of tang that engages with lock-bar is rough/unfinished
Terzuola OG Micarta - uneven finishing of micarta on one scales/each scale appears just a little bit differently finished from the other.
Terzuola FX-525 "Sicilian" - unfinished/rough-finished tang
Predator II FX-446 - unfinished/rough-finished tang, not the greatest action (smooth, but a bit stiff/loosening pivot introduced unacceptable blade play), early lockup prevented engagement of LAWKS safety until after a breaking-in period, one of the most poorly designed pocket clips I've ever encountered on a folding knife (looks ok, is somewhat functional, but screw placement and narrow height do not allow for acceptable clearance of pocket material, especially if pants have a thick hem)
I believe the rough tang thing is just a product of their manufacturing process; It doesn't seem to impact function, more of an aesthetic thing for me. I'm pretty forgiving of minor aesthetic issues so long as important concerns like, action, lockup, grind evenness, blade sharpness, overall F&F, centering, etc. are satisfactory. Where it counts, my Fox knives are pretty solid overall. If you like the design, I wouldn't hesitate to pick up a Fox..