I just picked up my vz-58 by the FAB ergonomic pistol grip. My rifle is a bit heavier with the addition of the aftermarket stock and EOTech. Hmm, no wiggle, stayed right on, no twisting, torquing, bending, tearing, nada. Even tried shaking it holding by grip only - hey, if it's gonna fall aprt, I'd need to know now instead of when "bad times" happen....nothing, solid as a rock.
Must be something specific to that rifle, or Canadian imports, dunno, but my D-Technik is just fine.